x86/purgatory: Remove LTO flags

PATCH Superseded Song Liu 2 participants 3 messages Sep 8, 2023

Subsystems (3)

x86 Live update kexec handover (KHO)

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Song Liu

author

2023-09-08 22:54 UTC #0 lore raw

PATCH 1/1 x86/purgatory: Remove LTO flags

With LTO enabled, ld.lld generates multiple .text sections for purgatory.ro:

$ readelf -S purgatory.ro  | grep " .text"
  [ 1] .text             PROGBITS         0000000000000000  00000040
  [ 7] .text.purgatory   PROGBITS         0000000000000000  000020e0
  [ 9] .text.warn        PROGBITS         0000000000000000  000021c0
  [13] .text.sha256_upda PROGBITS         0000000000000000  000022f0
  [15] .text.sha224_upda PROGBITS         0000000000000000  00002be0
  [17] .text.sha256_fina PROGBITS         0000000000000000  00002bf0
  [19] .text.sha224_fina PROGBITS         0000000000000000  00002cc0

This cause WARNING from kexec_purgatory_setup_sechdrs():

WARNING: CPU: 26 PID: 110894 at kernel/kexec_file.c:919
kexec_load_purgatory+0x37f/0x390

Fix this by disabling LTO for purgatory.

Fixes 8652d44f466a ("kexec: support purgatories with .text.hot sections")

Cc Ricardo Ribalda <[email protected]>

Cc [email protected]

Signed-off-by Song Liu <[email protected]>

---
AFAICT, x86 is the only arch that supports LTO and purgatory.

---
 arch/x86/purgatory/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

arch/x86/purgatory/Makefile +4 -0

index c2a29be35c01..9c0bff4992ea 100644
@@ -19,6 +19,10 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY
 # optimization flags.
 KBUILD_CFLAGS := $(filter-out -fprofile-sample-use=% -fprofile-use=%,$(KBUILD_CFLAGS))
 
+# When LTO is enabled, llvm emits many text sections, which is not supported
+# by kexec. Remove -flto=* flags.
+KBUILD_CFLAGS := $(filter-out -flto=%,$(KBUILD_CFLAGS))
+
 # When linking purgatory.ro with -r unresolved symbols are not checked,
 # also link a purgatory.chk binary without -r to check for unresolved symbols.
 PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib

Signature · 1 line

2.34.1

Nick Desaulniers

2023-09-08 22:59 UTC #1 lore raw

Quoted 37 lines · Song Liu

With LTO enabled, ld.lld generates multiple .text sections for purgatory.ro:
$ readelf -S purgatory.ro  | grep " .text"
  [ 1] .text             PROGBITS         0000000000000000  00000040
  [ 7] .text.purgatory   PROGBITS         0000000000000000  000020e0
  [ 9] .text.warn        PROGBITS         0000000000000000  000021c0
  [13] .text.sha256_upda PROGBITS         0000000000000000  000022f0
  [15] .text.sha224_upda PROGBITS         0000000000000000  00002be0
  [17] .text.sha256_fina PROGBITS         0000000000000000  00002bf0
  [19] .text.sha224_fina PROGBITS         0000000000000000  00002cc0
This cause WARNING from kexec_purgatory_setup_sechdrs():
WARNING: CPU: 26 PID: 110894 at kernel/kexec_file.c:919
kexec_load_purgatory+0x37f/0x390
Fix this by disabling LTO for purgatory.
Fixes 8652d44f466a ("kexec: support purgatories with .text.hot sections")
Cc Ricardo Ribalda <[email protected]>
Cc [email protected]
Cc [email protected]
Cc [email protected]
Signed-off-by Song Liu <[email protected]>
---
AFAICT, x86 is the only arch that supports LTO and purgatory.
---
 arch/x86/purgatory/Makefile | 4 ++++
 1 file changed, 4 insertions(+)
arch/x86/purgatory/Makefile +0 -0
index c2a29be35c01..9c0bff4992ea 100644

arch/x86/purgatory/Makefile CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY · line 24

Quoted 6 lines

arch/x86/purgatory/Makefile +3 -0

@@ -19,6 +19,10 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY
 # optimization flags.
 KBUILD_CFLAGS := $(filter-out -fprofile-sample-use=% -fprofile-use=%,$(KBUILD_CFLAGS))
 
+# When LTO is enabled, llvm emits many text sections, which is not supported
+# by kexec. Remove -flto=* flags.
+KBUILD_CFLAGS := $(filter-out -flto=%,$(KBUILD_CFLAGS))

Thanks for the patch!

Please prefer something akin to:
commit 6e20f18579c5 ("efi/libstub: disable LTO")

Please also CC Sami and [email protected] for v2.

Pretty sure we use a linker script to rejoin .text.* elsewhere in the kernel, but it doesn't look like x86 purgatory has one.

Quoted 7 lines

arch/x86/purgatory/Makefile +1 -0

+
 # When linking purgatory.ro with -r unresolved symbols are not checked,
 # also link a purgatory.chk binary without -r to check for unresolved symbols.
 PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib

Signature · 1 line

2.34.1

Song Liu

author

2023-09-08 23:10 UTC #2 lore raw

Quoted 42 lines · Nick Desaulniers

Quoted 40 lines · Song Liu
With LTO enabled, ld.lld generates multiple .text sections for purgatory.ro:
$ readelf -S purgatory.ro  | grep " .text"
  [ 1] .text             PROGBITS         0000000000000000  00000040
  [ 7] .text.purgatory   PROGBITS         0000000000000000  000020e0
  [ 9] .text.warn        PROGBITS         0000000000000000  000021c0
  [13] .text.sha256_upda PROGBITS         0000000000000000  000022f0
  [15] .text.sha224_upda PROGBITS         0000000000000000  00002be0
  [17] .text.sha256_fina PROGBITS         0000000000000000  00002bf0
  [19] .text.sha224_fina PROGBITS         0000000000000000  00002cc0
This cause WARNING from kexec_purgatory_setup_sechdrs():
WARNING: CPU: 26 PID: 110894 at kernel/kexec_file.c:919
kexec_load_purgatory+0x37f/0x390
Fix this by disabling LTO for purgatory.
Fixes 8652d44f466a ("kexec: support purgatories with .text.hot sections")
Cc Ricardo Ribalda <[email protected]>
Cc [email protected]
Cc [email protected]
Cc [email protected]
Signed-off-by Song Liu <[email protected]>
---
AFAICT, x86 is the only arch that supports LTO and purgatory.
---
 arch/x86/purgatory/Makefile | 4 ++++
 1 file changed, 4 insertions(+)
arch/x86/purgatory/Makefile +0 -0
index c2a29be35c01..9c0bff4992ea 100644
@@ -19,6 +19,10 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY
 # optimization flags.
 KBUILD_CFLAGS := $(filter-out -fprofile-sample-use=% -fprofile-use=%,$(KBUILD_CFLAGS))
 

Quoted 8 lines

arch/x86/purgatory/Makefile CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY · line 24
Quoted 3 lines
arch/x86/purgatory/Makefile +3 -0
+# When LTO is enabled, llvm emits many text sections, which is not supported
+# by kexec. Remove -flto=* flags.
+KBUILD_CFLAGS := $(filter-out -flto=%,$(KBUILD_CFLAGS))
Thanks for the patch!
Please prefer something akin to:
commit 6e20f18579c5 ("efi/libstub: disable LTO")

Thanks for the pointer! This does look better.

Thanks,
Song

Quoted 13 lines

Please also CC Sami and [email protected] for v2.
Pretty sure we use a linker script to rejoin .text.* elsewhere in the kernel, but it doesn't look like x86 purgatory has one.
Quoted 7 lines
arch/x86/purgatory/Makefile +1 -1
+
 # When linking purgatory.ro with -r unresolved symbols are not checked,
 # also link a purgatory.chk binary without -r to check for unresolved symbols.
 PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib
--
2.34.1