Update 'make fuzz-all' docs to reflect modern clang

PATCH Superseded Andrzej Hunt via GitGitGadget 4 participants 10 messages Feb 28, 2021 – Mar 10, 2021 Kbuild

lore

Share & tools

lore

Andrzej Hunt via GitGitGadget

author

2021-02-28 12:23 UTC #0 lore raw

PATCH 1/1 Update 'make fuzz-all' docs to reflect modern clang

From: Andrzej Hunt <[email protected]>

Clang no longer produces a libFuzzer.a, instead you can include libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in the example command for building fuzzers.

I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.

(On my system what used to be libFuzzer.a now lives under the following path,
which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )

Signed-off-by Andrzej Hunt <[email protected]>

---
Update 'make fuzz-all' docs to reflect modern clang

I would like to update the examples for 'make fuzz-all' to make it easier to build fuzzers locally.

This change should make it easier for the uninitiated to build fuzzers locally without first having to figure out what LIB_FUZZING_ENGINE is for.

ATB, Andrzej

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-889%2Fahunt%2Ffuzz-docs-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-889/ahunt/fuzz-docs-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/889

 Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Makefile +2 -2

index 9b1bde2e0e64..9f8f459f87b4 100644
@@ -3291,11 +3291,11 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:
+# An example command to build against libFuzzer from LLVM 11.0.0:
 #
 # make CC=clang CXX=clang++ \
 #      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      LIB_FUZZING_ENGINE=-fsanitize=fuzzer \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)

base-commit: 225365fb5195e804274ab569ac3cc4919451dc7f

Signature · 1 line

gitgitgadget

Josh Steadmon

2021-03-01 23:35 UTC #1 lore raw

Quoted 17 lines · Andrzej Hunt via GitGitGadget

From: Andrzej Hunt <[email protected]>
Clang no longer produces a libFuzzer.a, instead you can include libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in the example command for building fuzzers.
I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.
(On my system what used to be libFuzzer.a now lives under the following path,
which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )
Signed-off-by Andrzej Hunt <[email protected]>
---
Update 'make fuzz-all' docs to reflect modern clang

Quoted 8 lines

I would like to update the examples for 'make fuzz-all' to make it easier to build fuzzers locally.
This change should make it easier for the uninitiated to build fuzzers locally without first having to figure out what LIB_FUZZING_ENGINE is for.
ATB, Andrzej

Thanks for taking a look at this! This looked correct to me, but when I tried to run the fuzzers I got an error about "-fsanitize-coverage=trace-pc-guard" not being supported any longer. Looking at the LLVM 11.0.0 docs [1], I see that it recommends using "-fsanitize=fuzzer-no-link" instead (the "-no-link" is because we're also building executables that have their own main()).

So we'd also want to change CFLAGS to
"-fsanitize=fuzzer-no-link,address".

[1]: https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage

Andrzej Hunt

2021-03-04 15:29 UTC #2 lore raw

Quoted 3 lines · Josh Steadmon

Thanks for taking a look at this! This looked correct to me, but when I tried to run the fuzzers I got an error about "-fsanitize-coverage=trace-pc-guard" not being supported any longer.

Oops, I realised I was accidentally using clang 7 (instead of 11) locally. I can reproduce the same error with my copy of clang-11. Thanks for catching this!

Quoted 6 lines

Looking at the LLVM 11.0.0 docs [1], I see that it recommends using "-fsanitize=fuzzer-no-link" instead (the "-no-link" is because we're also building executables that have their own main()).
So we'd also want to change CFLAGS to
"-fsanitize=fuzzer-no-link,address".

I will fix this too!

I suspect that when I built without fuzzer-no-link, the fuzzer binaries included libFuzzer, but were missing whatever fuzzing-related instrumentation clang should have added. (Fortunately oss-fuzz seems to
be adding this to the CFLAGS automatically [1].)

[1] https://oss-fuzz-build-logs.storage.googleapis.com/log-74f40f33-f384-475b-b141-0e44afb272f5.txt

Andrzej Hunt via GitGitGadget

author

2021-03-04 15:29 UTC #3 lore raw

PATCH v2 1/1 Update 'make fuzz-all' docs to reflect modern clang

In reply to Andrzej Hunt via GitGitGadget

From: Andrzej Hunt <[email protected]>

Clang no longer produces a libFuzzer.a, instead you can include libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in the example command for building fuzzers.

We also add -fsanitize=fuzzer-no-link to ensure that all the required instrumentation is added when compiling git [1], and remove
-fsanitize-coverage=trace-pc-guard as it is deprecated.

I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.

(On my system: what used to be libFuzzer.a now lives under the following path,
which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )

[1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage

Signed-off-by Andrzej Hunt <[email protected]>

---
Update 'make fuzz-all' docs to reflect modern clang

I have updated my patch to:

* Remove -fsanitize-coverage=trace-pc-guard as it is deprecated.
* Add -fsanitize=fuzzer-no-link as per Josh's suggestion.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-889%2Fahunt%2Ffuzz-docs-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-889/ahunt/fuzz-docs-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/889

Range-diff vs v1:

1: d804b24907fd ! 1: f5b5a11966ca Update 'make fuzz-all' docs to reflect modern clang
@@ Commit message
libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in the example command for building fuzzers.

+ We also add -fsanitize=fuzzer-no-link to ensure that all the required
+ instrumentation is added when compiling git [1], and remove
+ -fsanitize-coverage=trace-pc-guard as it is deprecated.
+
I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.

- (On my system what used to be libFuzzer.a now lives under the following path,
+ (On my system: what used to be libFuzzer.a now lives under the following path,
which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )

+ [1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage
+

Signed-off-by Andrzej Hunt <[email protected]>

## Makefile ##
@@ Makefile: cover_db_html: cover_db
+# An example command to build against libFuzzer from LLVM 11.0.0:
#
# make CC=clang CXX=clang++ \
- # CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
+-# CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-# LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
-+# LIB_FUZZING_ENGINE=-fsanitize=fuzzer \
++# CFLAGS="-fsanitize=fuzzer-no-link,address" \
++# LIB_FUZZING_ENGINE="-fsanitize=fuzzer" \
# fuzz-all
#
FUZZ_CXXFLAGS ?= $(CFLAGS)

 Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Makefile +3 -3

index dd08b4ced01c..c7248ac6057b 100644
@@ -3292,11 +3292,11 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:
+# An example command to build against libFuzzer from LLVM 11.0.0:
 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
+#      LIB_FUZZING_ENGINE="-fsanitize=fuzzer" \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)

base-commit: f01623b2c9d14207e497b21ebc6b3ec4afaf4b46

Signature · 1 line

gitgitgadget

Junio C Hamano

2021-03-04 22:48 UTC #4 lore raw

Quoted 3 lines · Andrzej Hunt via GitGitGadget

From: Andrzej Hunt <[email protected]>
Subject: Re: [PATCH v2] Update 'make fuzz-all' docs to reflect modern clang

I'd retitte it to

Makefile: update 'make fuzz-all' docs to reflect modern clang

Quoted 2 lines

Clang no longer produces a libFuzzer.a, instead you can include libFuzzer by using -fsanitize=fuzzer.

Do we see two sentences here? IOW, s/, instead/. Instead/ is needed?

Quoted 6 lines

Therefore we should use
that in the example command for building fuzzers.
We also add -fsanitize=fuzzer-no-link to ensure that all the required instrumentation is added when compiling git [1], and remove
-fsanitize-coverage=trace-pc-guard as it is deprecated.

Without something like s/add/add to CFLAGS/, I found this a bit cryptic and failed to read what it wanted to do without looking at the patch text itself.

Quoted 6 lines

I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.
(On my system: what used to be libFuzzer.a now lives under the following path,
which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )

All nice things to have in the log message.

Quoted 12 lines

 Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Makefile +0 -1

index dd08b4ced01c..c7248ac6057b 100644
@@ -3292,11 +3292,11 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:

Makefile cover_db_html: cover_db · line 3302

Quoted 10 lines

Makefile +3 -2

+# An example command to build against libFuzzer from LLVM 11.0.0:
 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
+#      LIB_FUZZING_ENGINE="-fsanitize=fuzzer" \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)

LIB_FUZZING_ENGINE is used this way in the Makefile:

    $(FUZZ_PROGRAMS): all
            $(QUIET_LINK)$(CXX) $(FUZZ_CXXFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
                    $(XDIFF_OBJS) $(EXTLIBS) git.o [email protected] $(LIB_FUZZING_ENGINE) -o $@

and it is somewhat annoying to see a compiler/linker option that late on the command line, where readers would expect an object file or a library archive would appear. It makes me wonder if we should instead be doing something along the following line:

- empty LIB_FUZZING_ENGINE by default
- add -fsanitize=fuzzer names to FUZZ_CXXFLAGS

i.e.

Makefile +4 -3

index 4128b457e1..b5df76b33b 100644
@@ -3306,14 +3306,15 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:
+# An example command to build against libFuzzer from LLVM 11.0.0:
 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)
+FUZZ_CXXFLAGS += -fsanitize=fuzzer
+LIB_FUZZING_ENGINE =
 
 .PHONY: fuzz-all

In the meantime, I'll queue the version you sent as-is (modulo the retitling).

Thanks.

Andrzej Hunt

2021-03-08 17:06 UTC #5 lore raw

On 04/03/2021 23:48, Junio C Hamano wrote:>

Quoted 6 lines

LIB_FUZZING_ENGINE is used this way in the Makefile:

     $(FUZZ_PROGRAMS): all
             $(QUIET_LINK)$(CXX) $(FUZZ_CXXFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
                     $(XDIFF_OBJS) $(EXTLIBS) git.o [email protected] $(LIB_FUZZING_ENGINE) -o $@

Quoted 7 lines

and it is somewhat annoying to see a compiler/linker option that late on the command line, where readers would expect an object file or a library archive would appear. It makes me wonder if we should instead be doing something along the following line:
- empty LIB_FUZZING_ENGINE by default
- add -fsanitize=fuzzer names to FUZZ_CXXFLAGS

This sounds sensible to me, and will certainly simplify the use of
"make fuzz-all" by beginners - although I'm not sure just how useful the change would be since my understanding is that this target is almost exclusively used by oss-fuzz.

However I would prefer to wait for Josh's feedback before making such a change, as he is the owner of oss-fuzz's git integration [1], and as such is most likely to be affected by any changes to this target.

In the meantime I'll prepare an updated patch with a fixed commit message!

[1] https://github.com/google/oss-fuzz/blob/c41e46ffc8bc409bdfde0c0d2c97e1305f0c4106/projects/git/project.yaml#L3

Andrzej Hunt via GitGitGadget

author

2021-03-08 17:15 UTC #8 lore raw

PATCH v3 1/1 Makefile: update 'make fuzz-all' docs to reflect modern clang

In reply to Andrzej Hunt via GitGitGadget

From: Andrzej Hunt <[email protected]>

Clang no longer produces a libFuzzer.a. Instead, you can include libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in the example command for building fuzzers.

We also add -fsanitize=fuzzer-no-link to the CFLAGS to ensure that all the required instrumentation is added when compiling git [1], and remove
-fsanitize-coverage=trace-pc-guard as it is deprecated.

I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.

(On my system: what used to be libFuzzer.a now lives under the following
path, which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )

[1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage

Signed-off-by Andrzej Hunt <[email protected]>

---
Update 'make fuzz-all' docs to reflect modern clang

This version of the patch fixes the commit message as per Junio's feedback. Thank you!

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-889%2Fahunt%2Ffuzz-docs-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-889/ahunt/fuzz-docs-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/889

Range-diff vs v2:

1: f5b5a11966ca ! 1: bc0d8b615410 Update 'make fuzz-all' docs to reflect modern clang
@@ Metadata
Author: Andrzej Hunt <[email protected]>

## Commit message ##
- Update 'make fuzz-all' docs to reflect modern clang
+ Makefile: update 'make fuzz-all' docs to reflect modern clang

- Clang no longer produces a libFuzzer.a, instead you can include
- libFuzzer by using -fsanitize=fuzzer. Therefore we should use
- that in the example command for building fuzzers.
+ Clang no longer produces a libFuzzer.a. Instead, you can include
+ libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in
+ the example command for building fuzzers.

- We also add -fsanitize=fuzzer-no-link to ensure that all the required
- instrumentation is added when compiling git [1], and remove
+ We also add -fsanitize=fuzzer-no-link to the CFLAGS to ensure that all
+ the required instrumentation is added when compiling git [1], and remove
-fsanitize-coverage=trace-pc-guard as it is deprecated.

- I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to
- work in a wide range of reasonably modern clangs.
+ I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears
+ to work in a wide range of reasonably modern clangs.

- (On my system: what used to be libFuzzer.a now lives under the following path,
- which is tricky albeit not impossible for a novice such as myself to find:
+ (On my system: what used to be libFuzzer.a now lives under the following
+ path, which is tricky albeit not impossible for a novice such as myself
+ to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )

[1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage

 Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Makefile +3 -3

index dfb0f1000fa3..f3dc2178324e 100644
@@ -3299,11 +3299,11 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:
+# An example command to build against libFuzzer from LLVM 11.0.0:
 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
+#      LIB_FUZZING_ENGINE="-fsanitize=fuzzer" \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)

base-commit: be7935ed8bff19f481b033d0d242c5d5f239ed50

Signature · 1 line

gitgitgadget

Junio C Hamano

2021-03-08 18:28 UTC #6 lore raw

In reply to Andrzej Hunt

Quoted 6 lines · Andrzej Hunt

However I would prefer to wait for Josh's feedback before making such a change, as he is the owner of oss-fuzz's git integration [1], and as such is most likely to be affected by any changes to this target.
In the meantime I'll prepare an updated patch with a fixed commit message!

Makes sense. Let's wait and see what Josh says before going forward.

Josh Steadmon

2021-03-10 18:51 UTC #7 lore raw

In reply to Junio C Hamano

Quoted 60 lines · Junio C Hamano

Quoted 3 lines · Andrzej Hunt via GitGitGadget
From: Andrzej Hunt <[email protected]>
Subject: Re: [PATCH v2] Update 'make fuzz-all' docs to reflect modern clang
I'd retitte it to
Makefile: update 'make fuzz-all' docs to reflect modern clang
Quoted 2 lines
Clang no longer produces a libFuzzer.a, instead you can include libFuzzer by using -fsanitize=fuzzer.
Do we see two sentences here? IOW, s/, instead/. Instead/ is needed?
Quoted 6 lines
Therefore we should use
that in the example command for building fuzzers.
We also add -fsanitize=fuzzer-no-link to ensure that all the required instrumentation is added when compiling git [1], and remove
-fsanitize-coverage=trace-pc-guard as it is deprecated.
Without something like s/add/add to CFLAGS/, I found this a bit cryptic and failed to read what it wanted to do without looking at the patch text itself.
Quoted 6 lines
I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.
(On my system: what used to be libFuzzer.a now lives under the following path,
which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )
All nice things to have in the log message.
Quoted 12 lines
 Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
Makefile +0 -1
index dd08b4ced01c..c7248ac6057b 100644
@@ -3292,11 +3292,11 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:
Makefile cover_db_html: cover_db · line 3302
Quoted 10 lines
Makefile +3 -2
+# An example command to build against libFuzzer from LLVM 11.0.0:
 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
+#      LIB_FUZZING_ENGINE="-fsanitize=fuzzer" \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)
LIB_FUZZING_ENGINE is used this way in the Makefile:

Quoted 7 lines

    $(FUZZ_PROGRAMS): all
            $(QUIET_LINK)$(CXX) $(FUZZ_CXXFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
                    $(XDIFF_OBJS) $(EXTLIBS) git.o [email protected] $(LIB_FUZZING_ENGINE) -o $@
and it is somewhat annoying to see a compiler/linker option that late on the command line, where readers would expect an object file or a library archive would appear.

Yes, it appears that clang has changed how the fuzzing engine is selected, as this used to be just a library path (as you see in the diff). We might as well move this option up with the rest of the flags.

Quoted 18 lines

It makes me wonder if we should
instead be doing something along the following line:
- empty LIB_FUZZING_ENGINE by default
- add -fsanitize=fuzzer names to FUZZ_CXXFLAGS
i.e.
Makefile +1 -1
index 4128b457e1..b5df76b33b 100644
@@ -3306,14 +3306,15 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:
+# An example command to build against libFuzzer from LLVM 11.0.0:

Makefile cover_db_html: cover_db · line 3317

Quoted 10 lines

Makefile +3 -2

 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)
+FUZZ_CXXFLAGS += -fsanitize=fuzzer
+LIB_FUZZING_ENGINE =

I don't think we want to mess with FUZZ_CXXFLAGS, as oss-fuzz may be adding conflicting -fsanitize args here. Having LIB_FUZZING_ENGINE default to empty should be fine though.

Quoted 10 lines

Makefile +0 -0
 .PHONY: fuzz-all
 
 
In the meantime, I'll queue the version you sent as-is (modulo the retitling).
Thanks.

Josh Steadmon

2021-03-10 18:53 UTC #9 lore raw

Re: [PATCH v3] Makefile: update 'make fuzz-all' docs to reflect modern clang

In reply to Andrzej Hunt via GitGitGadget

Quoted 92 lines · Andrzej Hunt via GitGitGadget

From: Andrzej Hunt <[email protected]>
Clang no longer produces a libFuzzer.a. Instead, you can include libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in the example command for building fuzzers.
We also add -fsanitize=fuzzer-no-link to the CFLAGS to ensure that all the required instrumentation is added when compiling git [1], and remove
-fsanitize-coverage=trace-pc-guard as it is deprecated.
I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to work in a wide range of reasonably modern clangs.
(On my system: what used to be libFuzzer.a now lives under the following
path, which is tricky albeit not impossible for a novice such as myself to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )
[1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage
Signed-off-by Andrzej Hunt <[email protected]>
---
Update 'make fuzz-all' docs to reflect modern clang
This version of the patch fixes the commit message as per Junio's feedback. Thank you!
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-889%2Fahunt%2Ffuzz-docs-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-889/ahunt/fuzz-docs-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/889
Range-diff vs v2:
1: f5b5a11966ca ! 1: bc0d8b615410 Update 'make fuzz-all' docs to reflect modern clang
@@ Metadata
Author: Andrzej Hunt <[email protected]>
## Commit message ##
- Update 'make fuzz-all' docs to reflect modern clang
+ Makefile: update 'make fuzz-all' docs to reflect modern clang
- Clang no longer produces a libFuzzer.a, instead you can include
- libFuzzer by using -fsanitize=fuzzer. Therefore we should use
- that in the example command for building fuzzers.
+ Clang no longer produces a libFuzzer.a. Instead, you can include
+ libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in
+ the example command for building fuzzers.
- We also add -fsanitize=fuzzer-no-link to ensure that all the required
- instrumentation is added when compiling git [1], and remove
+ We also add -fsanitize=fuzzer-no-link to the CFLAGS to ensure that all
+ the required instrumentation is added when compiling git [1], and remove
-fsanitize-coverage=trace-pc-guard as it is deprecated.
- I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to
- work in a wide range of reasonably modern clangs.
+ I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears
+ to work in a wide range of reasonably modern clangs.
- (On my system: what used to be libFuzzer.a now lives under the following path,
- which is tricky albeit not impossible for a novice such as myself to find:
+ (On my system: what used to be libFuzzer.a now lives under the following
+ path, which is tricky albeit not impossible for a novice such as myself
+ to find:
/usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )
[1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage
 Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
Makefile +3 -3
index dfb0f1000fa3..f3dc2178324e 100644
@@ -3299,11 +3299,11 @@ cover_db_html: cover_db
 # are not necessarily appropriate for general builds, and that vary greatly
 # depending on the compiler version used.
 #
-# An example command to build against libFuzzer from LLVM 4.0.0:
+# An example command to build against libFuzzer from LLVM 11.0.0:
 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
-#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
+#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
+#      LIB_FUZZING_ENGINE="-fsanitize=fuzzer" \
 #      fuzz-all
 #
 FUZZ_CXXFLAGS ?= $(CFLAGS)

Quoted 3 lines

base-commit: be7935ed8bff19f481b033d0d242c5d5f239ed50
Signature · 1 line
gitgitgadget

This version looks good to me, although you may also want to make the changes Junio suggested regarding LIB_FUZZING_ENGINE.

Thanks!