efi: Fix free_end build warning
PATCH 1/1 efi: Fix free_end build warning
Initialize the free_end variable to zero. Fixes build warnings like these:
arch/arm64/kernel/efi.c: warning: ?free_end? may be used uninitialized in this function
---
Got this with the latest arm64/for-next/core branch. Please consider.
-Geoff
arch/arm64/kernel/efi.c | 1 + 1 file changed, 1 insertion(+)
arch/arm64/kernel/efi.c +1 -0
@@ -239,6 +239,7 @@ static void __init free_boot_services(void)* want to keep for UEFI. */ + free_end =0 ; keep_end =0 ; free_start =0 ;
Signature · 1 line
1.9.1
PATCH 1/1 efi: Fix free_end build warning
Hi Geoff,
Quoted 19 lines · Geoff Levand
Initialize the
free_endvariable to zero. Fixes build warnings like these:
arch/arm64/kernel/efi.c: warning: ?free_end? may be used uninitialized in this functionSigned-off-by Geoff Levand <[email protected]>---
Got this with the latest arm64/for-next/core branch. Please consider.(quoted diff) +0
-1-Geoff arch/arm64/kernel/efi.c | 1 + 1 file changed, 1 insertion(+)arch/arm64/kernel/efi.c +0
-0
arch/arm64/kernel/efi.c static void __init free_boot_services(void) · line 244
Quoted 6 lines
arch/arm64/kernel/efi.c +1
-0@@ -239,6 +239,7 @@ static void __init free_boot_services(void)* want to keep for UEFI. */ + free_end =0 ; keep_end =0 ; free_start =0 ;
Do you have any idea how GCC arrives at this conclusion? I can't see a path through that function where we use free_end without initialising it.
Does something like the patch below help?
Will
--->8
arch/arm64/kernel/efi.c +4 -5
@@ -271,17 +271,16 @@ static void __init free_boot_services(void) size = npages <<PAGE_SHIFT ;if (free_start) { -if (paddr <= free_end) - free_end = paddr + size; -else { +if (paddr > free_end) { total_freed +=free_region (free_start, free_end); free_start = paddr; - free_end = paddr + size; } }else { free_start = paddr; - free_end = paddr + size; } + + free_end = paddr + size; +if (free_start < keep_end) { free_start +=PAGE_SIZE ;if (free_start >= free_end)
PATCH 1/1 efi: Fix free_end build warning
Hi Will,
Quoted 2 lines · Will Deacon
Do you have any idea how GCC arrives at this conclusion? I can't see a path through that function where we use
free_endwithout initialising it.
I've seen it warn like this before, when it shouldn't. I guess -Wmaybe-uninitialized makes it more conservative.
Using:
aarch64-linux-gnu-gcc (Ubuntu/Linaro 4.8.2-13ubuntu1) 4.8.2 20140110 (prerelease) [ibm/gcc-4_8-branch merged from gcc-4_8-branch, revision 205847]
Quoted 1 line
Does something like the patch below help?
Here is the full output, for-next/core gives:
/home/geoff/projects/linaro/git/linux-kexec/arch/arm64/kernel/efi.c:281:31: warning: ?free_end? may be used uninitialized in this function [-Wmaybe-uninitialized]
total_freed += free_region(free_start, free_end);
^
/home/geoff/projects/linaro/git/linux-kexec/arch/arm64/kernel/efi.c:225:28: note: ?free_end? was declared here
u64 keep_end, free_start, free_end;
^Your mod gives:
/home/geoff/projects/linaro/git/linux-kexec/arch/arm64/kernel/efi.c:279:31: warning: ?free_end? may be used uninitialized in this function [-Wmaybe-uninitialized]
total_freed += free_region(free_start, free_end);
^
/home/geoff/projects/linaro/git/linux-kexec/arch/arm64/kernel/efi.c:225:28: note: ?free_end? was declared here
u64 keep_end, free_start, free_end;
^So about the same.
-Geoff
PATCH 1/1 efi: Fix free_end build warning
In reply to Geoff Levand[Adding original authors]
Quoted 19 lines · Geoff Levand
Initialize the
free_endvariable to zero. Fixes build warnings like these:
arch/arm64/kernel/efi.c: warning: ?free_end? may be used uninitialized in this functionSigned-off-by Geoff Levand <[email protected]>---
Got this with the latest arm64/for-next/core branch. Please consider.(quoted diff) +0
-1-Geoff arch/arm64/kernel/efi.c | 1 + 1 file changed, 1 insertion(+)arch/arm64/kernel/efi.c +0
-0
arch/arm64/kernel/efi.c static void __init free_boot_services(void) · line 244
Quoted 6 lines
arch/arm64/kernel/efi.c +1
-0@@ -239,6 +239,7 @@ static void __init free_boot_services(void)* want to keep for UEFI. */ + free_end =0 ; keep_end =0 ; free_start =0 ;
Whilst I can't see how free_end gets used uninitialized in this function, the code is really hard to read and I'd like to get an Ack from one of the people on CC before merging this, just in case GCC is actually telling us something useful for a change.
Will
PATCH 1/1 efi: Fix free_end build warning
Quoted 25 lines · Will Deacon
[Adding original authors]
Quoted 22 lines · Geoff Levand
Initialize the
free_endvariable to zero. Fixes build warnings like these:
arch/arm64/kernel/efi.c: warning: ?free_end? may be used uninitialized in this functionSigned-off-by Geoff Levand <[email protected]>---
Got this with the latest arm64/for-next/core branch. Please consider.(quoted diff) +0
-1-Geoff arch/arm64/kernel/efi.c | 1 + 1 file changed, 1 insertion(+)arch/arm64/kernel/efi.c +0
-0@@ -239,6 +239,7 @@ static void __init free_boot_services(void)* want to keep for UEFI. */
Quoted 9 lines
arch/arm64/kernel/efi.c static void __init free_boot_services(void) · line 244
Quoted 3 lines
arch/arm64/kernel/efi.c +1
-0+ free_end =0 ; keep_end =0 ; free_start =0 ;Whilst I can't see how
free_endgets used uninitialized in this function, the code is really hard to read and I'd like to get an Ack from one of the people on CC before merging this, just in case GCC is actually telling us something useful for a change.
We are planning to remove this code entirely in the 3.20 timeframe. Freeing boot services will not be necessary any longer once we stop reserving it in the first place, and I agree that the function is hard to read. Also, it depends on the UEFI memory map being sorted, which is not mandated by the spec so we can't actually rely on it. (Even if it usually is the case)
So I don't object to this patch, if the warning is bothering people, but perhaps we can just wait for the warning to go away once the new stuff lands.
Signature · 1 line
Ard.
PATCH 1/1 efi: Fix free_end build warning
Quoted 43 lines · Ard Biesheuvel
Quoted 25 lines · Will Deacon
[Adding original authors]
Quoted 22 lines · Geoff Levand
Initialize the
free_endvariable to zero. Fixes build warnings like these:
arch/arm64/kernel/efi.c: warning: ?free_end? may be used uninitialized in this functionSigned-off-by Geoff Levand <[email protected]>---
Got this with the latest arm64/for-next/core branch. Please consider.(quoted diff) +0
-1-Geoff arch/arm64/kernel/efi.c | 1 + 1 file changed, 1 insertion(+)arch/arm64/kernel/efi.c +0
-0@@ -239,6 +239,7 @@ static void __init free_boot_services(void)* want to keep for UEFI. */ Quoted 9 lines
arch/arm64/kernel/efi.c static void __init free_boot_services(void) · line 244
Quoted 3 lines
arch/arm64/kernel/efi.c +1
-0+ free_end =0 ; keep_end =0 ; free_start =0 ;Whilst I can't see how
free_endgets used uninitialized in this function, the code is really hard to read and I'd like to get an Ack from one of the people on CC before merging this, just in case GCC is actually telling us something useful for a change.We are planning to remove this code entirely in the 3.20 timeframe. Freeing boot services will not be necessary any longer once we stop reserving it in the first place, and I agree that the function is hard to read. Also, it depends on the UEFI memory map being sorted, which is not mandated by the spec so we can't actually rely on it. (Even if it usually is the case)
Quoted 3 lines
So I don't object to this patch, if the warning is bothering people, but perhaps we can just wait for the warning to go away once the new stuff lands.
Ok, thanks Ard. I think I'll leave it alone for now, then.
Will