[tip: x86/core] x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

[tip-bot2 for Petr Pavlu]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     973ab2d61f33dc85212c486e624af348c4eeb5c9
Gitweb:        https://git.kernel.org/tip/973ab2d61f33dc85212c486e624af348c4eeb5c9
Author:        Petr Pavlu <petr.pavlu@xxxxxxxx>
AuthorDate:    Tue, 11 Jul 2023 11:19:51 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 02 Aug 2023 16:27:07 +02:00

x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

Linker script arch/x86/kernel/vmlinux.lds.S matches the thunk sections
".text.__x86.*" from arch/x86/lib/retpoline.S as follows:

.text {
  [...]
  TEXT_TEXT
  [...]
  __indirect_thunk_start = .;
  *(.text.__x86.*)
  __indirect_thunk_end = .;
  [...]
}

Macro TEXT_TEXT references TEXT_MAIN which normally expands to only
".text". However, with CONFIG_LTO_CLANG, TEXT_MAIN becomes
".text .text.[0-9a-zA-Z_]*" which wrongly matches also the thunk
sections. The output layout is then different than expected. For
instance, the currently defined range [__indirect_thunk_start,
__indirect_thunk_end] becomes empty.

Prevent the problem by using ".." as the first separator, for example,
".text..__x86.indirect_thunk". This pattern is utilized by other
explicit section names which start with one of the standard prefixes,
such as ".text" or ".data", and that need to be individually selected in
the linker script.

Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO")
Signed-off-by: Petr Pavlu <petr.pavlu@xxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230711091952.27944-2-petr.pavlu@xxxxxxxx
---
 arch/x86/kernel/vmlinux.lds.S | 2 +-
 arch/x86/lib/retpoline.S      | 4 ++--
 tools/objtool/check.c         | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 03c885d..a4cd04c 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -134,7 +134,7 @@ SECTIONS
 		SOFTIRQENTRY_TEXT
 #ifdef CONFIG_RETPOLINE
 		__indirect_thunk_start = .;
-		*(.text.__x86.*)
+		*(.text..__x86.*)
 		__indirect_thunk_end = .;
 #endif
 		STATIC_CALL_TEXT
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 3fd066d..3bea963 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -12,7 +12,7 @@
 #include <asm/percpu.h>
 #include <asm/frame.h>
 
-	.section .text.__x86.indirect_thunk
+	.section .text..__x86.indirect_thunk
 
 
 .macro POLINE reg
@@ -131,7 +131,7 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array)
  */
 #ifdef CONFIG_RETHUNK
 
-	.section .text.__x86.return_thunk
+	.section .text..__x86.return_thunk
 
 /*
  * Safety details here pertain to the AMD Zen{1,2} microarchitecture:
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8936a05..e096eb3 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -389,7 +389,7 @@ static int decode_instructions(struct objtool_file *file)
 		if (!strcmp(sec->name, ".noinstr.text") ||
 		    !strcmp(sec->name, ".entry.text") ||
 		    !strcmp(sec->name, ".cpuidle.text") ||
-		    !strncmp(sec->name, ".text.__x86.", 12))
+		    !strncmp(sec->name, ".text..__x86.", 12))
 			sec->noinstr = true;
 
 		/*