Re: [PATCH v4 0/4] kallsyms: embed source file:line info in kernel stack traces

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 22 Mar 2026 09:15:39 -0400 Sasha Levin <sashal@kernel.org> wrote:

> This series adds CONFIG_KALLSYMS_LINEINFO, which embeds source file:line
> information directly in the kernel image so that stack traces annotate
> every frame with the originating source location - no external tools, no
> debug symbols at runtime, and safe to use in NMI/panic context.

Thanks, I've updated mm.git's mm-nonmm-unstable branch to this version.

> Changes since v3
> =================
> 
> - Remove redundant gen_lineinfo entry in scripts/Makefile for
>   CONFIG_KALLSYMS_LINEINFO_MODULES (depends on CONFIG_KALLSYMS_LINEINFO
>   which already builds it). (Reported by Petr Pavlu)
> 
> - Use R_* constants from <elf.h> instead of hardcoded relocation type
>   values in r_type_abs32(). (Reported by Petr Pavlu)
> 
> - Simplify duplicated-path detection in make_relative(): replace loop
>   over every '/' with a direct midpoint check, since true path
>   duplication always splits at len/2. (Suggested by Petr Pavlu)
> 
> - Fix comment in process_dwarf(): sections in ET_REL objects have
>   sh_addr == 0 and therefore overlapping address ranges; this is
>   expected behavior, not a "may" situation. (Reported by Petr Pavlu)
> 
> - Use U32_MAX instead of UINT_MAX for the module raw_offset bounds
>   check, matching the u32 type of the addrs array.
>   (Reported by Petr Pavlu)
> 
> - Document the assumption that .text is at the start of the MOD_TEXT
>   segment in module_lookup_lineinfo(). A proper fix using ELF
>   relocations is planned for a future series.
>   (Reported by Petr Pavlu)
> 
> - Wrap -fno-inline-functions-called-once in $(call cc-option,...) for
>   clang compatibility. Clang does not support this GCC-specific flag;
>   the noinline attribute is sufficient.

Here's how v3 altered mm.git:


 kernel/module/kallsyms.c |    8 +++++--
 lib/tests/Makefile       |    2 -
 scripts/Makefile         |    1 
 scripts/gen_lineinfo.c   |   40 +++++++++++++++++--------------------
 4 files changed, 26 insertions(+), 25 deletions(-)

--- a/kernel/module/kallsyms.c~b
+++ a/kernel/module/kallsyms.c
@@ -547,13 +547,17 @@ bool module_lookup_lineinfo(struct modul
 	if (hdr->files_size < hdr->num_files * sizeof(u32))
 		return false;
 
-	/* Compute offset from module .text base */
+	/*
+	 * Compute offset from module .text base.
+	 * NOTE: This assumes .text is at the start of the MOD_TEXT segment.
+	 * A proper fix would use ELF relocations to reference .text directly.
+	 */
 	text_base = (unsigned long)mod->mem[MOD_TEXT].base;
 	if (addr < text_base)
 		return false;
 
 	raw_offset = addr - text_base;
-	if (raw_offset > UINT_MAX)
+	if (raw_offset > U32_MAX)
 		return false;
 
 	tbl.blk_addrs	= base + hdr->blocks_offset;
--- a/lib/tests/Makefile~b
+++ a/lib/tests/Makefile
@@ -36,7 +36,7 @@ obj-$(CONFIG_LIVEUPDATE_TEST) += liveupd
 CFLAGS_longest_symbol_kunit.o += $(call cc-disable-warning, missing-prototypes)
 obj-$(CONFIG_LONGEST_SYM_KUNIT_TEST) += longest_symbol_kunit.o
 
-CFLAGS_lineinfo_kunit.o += -fno-inline-functions-called-once
+CFLAGS_lineinfo_kunit.o += $(call cc-option,-fno-inline-functions-called-once)
 obj-$(CONFIG_LINEINFO_KUNIT_TEST) += lineinfo_kunit.o
 
 obj-$(CONFIG_MEMCPY_KUNIT_TEST) += memcpy_kunit.o
--- a/scripts/gen_lineinfo.c~b
+++ a/scripts/gen_lineinfo.c
@@ -206,14 +206,11 @@ static const char *make_relative(const c
 	 */
 	{
 		size_t len = strlen(path);
+		size_t mid = len / 2;
 
-		for (p = path; (p = strchr(p, '/')) != NULL; p++) {
-			size_t prefix = p - path;
-			size_t rest = len - prefix - 1;
-
-			if (rest == prefix && !memcmp(path, p + 1, prefix))
-				return p + 1;
-		}
+		if (len > 1 && path[mid] == '/' &&
+		    !memcmp(path, path + mid + 1, mid))
+			return path + mid + 1;
 	}
 
 	/*
@@ -340,17 +337,17 @@ static void find_text_section_range(Elf
 static unsigned int r_type_abs32(unsigned int e_machine)
 {
 	switch (e_machine) {
-	case EM_X86_64:		return 10;	/* R_X86_64_32 */
-	case EM_386:		return 1;	/* R_386_32 */
-	case EM_AARCH64:	return 258;	/* R_AARCH64_ABS32 */
-	case EM_ARM:		return 2;	/* R_ARM_ABS32 */
-	case EM_RISCV:		return 1;	/* R_RISCV_32 */
-	case EM_S390:		return 4;	/* R_390_32 */
-	case EM_MIPS:		return 2;	/* R_MIPS_32 */
-	case EM_PPC64:		return 1;	/* R_PPC64_ADDR32 */
-	case EM_PPC:		return 1;	/* R_PPC_ADDR32 */
-	case EM_LOONGARCH:	return 1;	/* R_LARCH_32 */
-	case EM_PARISC:		return 1;	/* R_PARISC_DIR32 */
+	case EM_X86_64:		return R_X86_64_32;
+	case EM_386:		return R_386_32;
+	case EM_AARCH64:	return R_AARCH64_ABS32;
+	case EM_ARM:		return R_ARM_ABS32;
+	case EM_RISCV:		return R_RISCV_32;
+	case EM_S390:		return R_390_32;
+	case EM_MIPS:		return R_MIPS_32;
+	case EM_PPC64:		return R_PPC64_ADDR32;
+	case EM_PPC:		return R_PPC_ADDR32;
+	case EM_LOONGARCH:	return R_LARCH_32;
+	case EM_PARISC:		return R_PARISC_DIR32;
 	default:		return 0;
 	}
 }
@@ -492,9 +489,10 @@ static void process_dwarf(Dwarf *dwarf,
 
 			/*
 			 * In module mode, keep only .text addresses.
-			 * In ET_REL .ko files, .init.text/.exit.text may
-			 * overlap with .text address ranges, so we must
-			 * explicitly check against the .text bounds.
+			 * In ET_REL .ko files, .text, .init.text and
+			 * .exit.text all have sh_addr == 0 and therefore
+			 * overlapping address ranges.  Explicitly check
+			 * against the .text bounds.
 			 */
 			if (module_mode && text_section_end > text_section_start &&
 			    (addr < text_section_start || addr >= text_section_end))
--- a/scripts/Makefile~b
+++ a/scripts/Makefile
@@ -5,7 +5,6 @@
 
 hostprogs-always-$(CONFIG_KALLSYMS)			+= kallsyms
 hostprogs-always-$(CONFIG_KALLSYMS_LINEINFO)		+= gen_lineinfo
-hostprogs-always-$(CONFIG_KALLSYMS_LINEINFO_MODULES)	+= gen_lineinfo
 hostprogs-always-$(BUILD_C_RECORDMCOUNT)		+= recordmcount
 hostprogs-always-$(CONFIG_BUILDTIME_TABLE_SORT)		+= sorttable
 hostprogs-always-$(CONFIG_ASN1)				+= asn1_compiler
_