From: Chuck Lever Date: Mon, 23 Mar 2026 15:58:04 +0000 (-0400) Subject: perf tools: Fix module symbol resolution for non-zero .text sh_addr X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9a82bfde4775b7a87cd1a7e791f46f83ae442848;p=thirdparty%2Flinux.git perf tools: Fix module symbol resolution for non-zero .text sh_addr When perf resolves symbols from kernel module ELF files (ET_REL), it converts symbol addresses to file offsets so that sample IPs can be matched to the correct symbol. The conversion adjusts each symbol's st_value: sym->st_value -= shdr->sh_addr - shdr->sh_offset; For vmlinux (ET_EXEC), st_value is a virtual address and sh_addr is the section's virtual base, so subtracting sh_addr and adding sh_offset correctly yields a file offset. For kernel modules (ET_REL), st_value is a section-relative offset. The module loader ignores sh_addr entirely and places symbols at module_base + st_value. Converting to file offset requires only adding sh_offset; subtracting sh_addr introduces an error equal to sh_addr bytes. When .text has sh_addr == 0 -- the historical norm for simple modules -- both formulas produce the same result and the bug is latent. As modules gain more metadata sections before .text (.note, .static_call.text, etc.), the linker assigns .text a non-zero sh_addr, exposing the defect. For example, nfsd.ko on this kernel has sh_addr=0xa80, kvm-intel.ko has sh_addr=0x1e90. The effect is that all .text symbols in affected modules shift by sh_addr bytes relative to sample IPs, causing perf report to attribute samples to incorrect, nearby symbols. This was observed as 13% of LLC-load-miss samples misattributed to nfsd_file_get_dio_attrs when the actual hot function was nfsd_cache_lookup, approximately 0xa80 bytes away in the symbol table. Use the existing dso__rel() flag (already set for ET_REL modules) to select the correct adjustment: add sh_offset for ET_REL, subtract (sh_addr - sh_offset) for ET_EXEC/ET_DYN. Fixes: 0131c4ec794a ("perf tools: Make it possible to read object code from kernel modules") Signed-off-by: Chuck Lever Reviewed-by: Ian Rogers Tested-by: Thomas Richter Signed-off-by: Namhyung Kim --- diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c index 3cd4e5a03cc5d..7afa8a1171396 100644 --- a/tools/perf/util/symbol-elf.c +++ b/tools/perf/util/symbol-elf.c @@ -1354,8 +1354,12 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map, char dso_name[PATH_MAX]; /* Adjust symbol to map to file offset */ - if (adjust_kernel_syms) - sym->st_value -= shdr->sh_addr - shdr->sh_offset; + if (adjust_kernel_syms) { + if (dso__rel(dso)) + sym->st_value += shdr->sh_offset; + else + sym->st_value -= shdr->sh_addr - shdr->sh_offset; + } if (strcmp(section_name, (dso__short_name(curr_dso) + dso__short_name_len(dso))) == 0) return 0;