-flto* implies -ffunction-sections. 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.
We could also fix this with an explicit linker script to rejoin .text.*
sections back into .text. However, given the benefit of LTOing pugatory
is small, simply disable the production of more .text.* sections for now.
Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
Cc: Ricardo Ribalda <[email protected]>
Cc: Sami Tolvanen <[email protected]>
Cc: [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.
Changes in v3:
1. Fix "Fixes" tag. (Nick Desaulniers)
2. Add description of an alternative fix, with linker script.
(Nick Desaulniers)
Changes in v2:
1. Use CC_FLAGS_LTO instead of hardcode -flto. (Nick Desaulniers)
---
arch/x86/purgatory/Makefile | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index c2a29be35c01..08aa0f25f12a 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 $(CC_FLAGS_LTO),$(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
On Thu, Sep 14, 2023 at 10:02 AM Song Liu <[email protected]> wrote:
>
> -flto* implies -ffunction-sections. 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.
>
> We could also fix this with an explicit linker script to rejoin .text.*
> sections back into .text. However, given the benefit of LTOing pugatory
s/pugatory/purgatory/
(maybe the x86 maintainers can apply that fixup if/when picked up)
> is small, simply disable the production of more .text.* sections for now.
>
> Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
> Cc: Ricardo Ribalda <[email protected]>
> Cc: Sami Tolvanen <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Song Liu <[email protected]>
Thanks for the patch!
Reviewed-by: Nick Desaulniers <[email protected]>
>
> ---
> AFAICT, x86 is the only arch that supports LTO and purgatory.
>
> Changes in v3:
> 1. Fix "Fixes" tag. (Nick Desaulniers)
> 2. Add description of an alternative fix, with linker script.
> (Nick Desaulniers)
>
> Changes in v2:
> 1. Use CC_FLAGS_LTO instead of hardcode -flto. (Nick Desaulniers)
> ---
> arch/x86/purgatory/Makefile | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index c2a29be35c01..08aa0f25f12a 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 $(CC_FLAGS_LTO),$(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
>
--
Thanks,
~Nick Desaulniers
On Thu, Sep 14, 2023 at 10:02 AM Song Liu <[email protected]> wrote:
>
> -flto* implies -ffunction-sections. 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.
>
> We could also fix this with an explicit linker script to rejoin .text.*
> sections back into .text. However, given the benefit of LTOing pugatory
> is small, simply disable the production of more .text.* sections for now.
>
> Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
> Cc: Ricardo Ribalda <[email protected]>
> Cc: Sami Tolvanen <[email protected]>
> Cc: [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.
>
> Changes in v3:
> 1. Fix "Fixes" tag. (Nick Desaulniers)
> 2. Add description of an alternative fix, with linker script.
> (Nick Desaulniers)
>
> Changes in v2:
> 1. Use CC_FLAGS_LTO instead of hardcode -flto. (Nick Desaulniers)
> ---
> arch/x86/purgatory/Makefile | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index c2a29be35c01..08aa0f25f12a 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 $(CC_FLAGS_LTO),$(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
LGTM, thanks for the patch!
Reviewed-by: Sami Tolvanen <[email protected]>
Sami
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: f7d2101197488fdd2106ca21346733562f398765
Gitweb: https://git.kernel.org/tip/f7d2101197488fdd2106ca21346733562f398765
Author: Song Liu <[email protected]>
AuthorDate: Thu, 14 Sep 2023 10:01:38 -07:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Fri, 15 Sep 2023 10:31:26 +02:00
x86/purgatory: Remove LTO flags
-flto* implies -ffunction-sections. 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 causes 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.
[ AFAICT, x86 is the only arch that supports LTO and purgatory. ]
We could also fix this with an explicit linker script to rejoin .text.*
sections back into .text. However, given the benefit of LTOing purgatory
is small, simply disable the production of more .text.* sections for now.
Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
Signed-off-by: Song Liu <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Reviewed-by: Sami Tolvanen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/purgatory/Makefile | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index c2a29be..08aa0f2 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 $(CC_FLAGS_LTO),$(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
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 75b2f7e4c9e0fd750a5a27ca9736d1daa7a3762a
Gitweb: https://git.kernel.org/tip/75b2f7e4c9e0fd750a5a27ca9736d1daa7a3762a
Author: Song Liu <[email protected]>
AuthorDate: Thu, 14 Sep 2023 10:01:38 -07:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Sun, 17 Sep 2023 09:49:03 +02:00
x86/purgatory: Remove LTO flags
-flto* implies -ffunction-sections. 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 causes 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.
[ AFAICT, x86 is the only arch that supports LTO and purgatory. ]
We could also fix this with an explicit linker script to rejoin .text.*
sections back into .text. However, given the benefit of LTOing purgatory
is small, simply disable the production of more .text.* sections for now.
Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
Signed-off-by: Song Liu <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Reviewed-by: Sami Tolvanen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/purgatory/Makefile | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index c2a29be..08aa0f2 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 $(CC_FLAGS_LTO),$(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