2023-09-09 00:40:18

by Song Liu

Subject: [PATCH] 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]
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(+)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index c2a29be35c01..9c0bff4992ea 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -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
--
2.34.1

2023-09-09 00:41:02

by Song Liu

Subject: Re: [PATCH] x86/purgatory: Remove LTO flags

On Fri, Sep 8, 2023 at 3:59 PM Nick Desaulniers <[email protected]> wrote:
>
> On Fri, Sep 08, 2023 at 03:53:53PM -0700, Song Liu wrote:
> > 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(+)
> >
> > diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> > index c2a29be35c01..9c0bff4992ea 100644
> > --- a/arch/x86/purgatory/Makefile
> > +++ b/arch/x86/purgatory/Makefile
> > @@ -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")

Thanks for the pointer! This does look better.

Thanks,
Song

>
> 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.
>
> > +
> > # 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
> >