[PATCH 1/4] perf symbols: Fix broken ELF_C_READ_MMAP fallback guard

[Alireza Haghdoost via B4 Relay <devnull+haghdoost.uber.com@kernel.org>]

From: Alireza Haghdoost <haghdoost@uber.com>

This patch makes perf mmap ELF files.  This was the intended behavior,
regressed by commit 22dd1ac91a77 ("tools: Remove feature-libelf-mmap
feature detection").  ELF_C_READ_MMAP is an Elf_Cmd enumerator, not a
preprocessor macro, so the #ifdef is false on every libelf that provides
it.  objtool uses ELF_C_READ_MMAP without an #ifdef guard and has been
fine for five years.

elf_getdata() still allocates when translation is needed (32-on-64 or
cross-endian), and libelf falls back to internal reads on non-seekable
fds.

Fixes: 22dd1ac91a77 ("tools: Remove feature-libelf-mmap feature detection")
Signed-off-by: Alireza Haghdoost <haghdoost@uber.com>
Assisted-by: Kimi:K3
---
 tools/perf/util/symbol.h | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index d0bac824c79c..e5cef16b240d 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -57,15 +57,8 @@ static inline bool is_livepatch_symbol(const char *str)
 	return strstarts(str, KLP_SYM_PREFIX);
 }
 
-/*
- * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP;
- * for newer versions we can use mmap to reduce memory usage:
- */
-#ifdef ELF_C_READ_MMAP
-# define PERF_ELF_C_READ_MMAP ELF_C_READ_MMAP
-#else
-# define PERF_ELF_C_READ_MMAP ELF_C_READ
-#endif
+/* libelf falls back to internal reads when mmap fails (e.g. non-seekable fd). */
+#define PERF_ELF_C_READ_MMAP ELF_C_READ_MMAP
 
 #ifdef HAVE_LIBELF_SUPPORT
 Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,

-- 
Git-155)