kernel/tools/perf/util/genelf.c, branch master

perf genelf: Switch from SHA-1 to BLAKE2s for build ID generation

2026-01-13T20:03:28Z

Recent patches [1] [2] added an implementation of SHA-1 to perf and made it be used for build ID generation. I had understood the choice of SHA-1, which is a legacy algorithm, to be for backwards compatibility. It turns out, though, that there's no backwards compatibility requirement here other than the size of the build ID field, which is fixed at 20 bytes. Not only did the hash algorithm already change (from MD5 to SHA-1), but the inputs to the hash changed too: from 'load_addr || code' to just 'code', and now again to 'code || symtab || strsym' [3]. Different linkers generate different build IDs, with the LLVM linker using BLAKE3 hashes for example [4]. Therefore, we might as well switch to a more modern algorithm. Let's go with BLAKE2s. It's faster than SHA-1, isn't cryptographically broken, is easier to implement than BLAKE3, and the kernel's implementation in lib/crypto/blake2s.c is easily borrowed. It also natively supports variable-length hashes, so it can directly produce the needed 20 bytes. Also make the following additional improvements: - Hash the three inputs incrementally, so they don't all have to be concatenated into one buffer. - Add tag/length prefixes to each of the three inputs, so that distinct input tuples reliably result in distinct hashes. [1] https://lore.kernel.org/linux-perf-users/20250521225307.743726-1-yuzhuo@google.com/ [2] https://lore.kernel.org/linux-perf-users/20250625202311.23244-1-ebiggers@kernel.org/ [3] https://lore.kernel.org/linux-perf-users/20251125080748.461014-1-namhyung@kernel.org/ [4] https://github.com/llvm/llvm-project/commit/d3e5b6f7539b86995aef6e2075c1edb3059385ce Signed-off-by: Eric Biggers Tested-by: Ian Rogers Acked-by: Namhyung Kim Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Fangrui Song Cc: Ingo Molnar Cc: James Clark Cc: Jason A. Donenfeld Cc: Jiri Olsa Cc: Mark Rutland Cc: Pablo Galindo Cc: Peter Zijlstra Signed-off-by: Arnaldo Carvalho de Melo

perf jitdump: Add sym/str-tables to build-ID generation

2025-12-03T00:06:57Z

It was reported that python backtrace with JIT dump was broken after the change to built-in SHA-1 implementation. It seems python generates the same JIT code for each function. They will become separate DSOs but the contents are the same. Only difference is in the symbol name. But this caused a problem that every JIT'ed DSOs will have the same build-ID which makes perf confused. And it resulted in no python symbols (from JIT) in the output. Looking back at the original code before the conversion, it used the load_addr as well as the code section to distinguish each DSO. But it'd be better to use contents of symtab and strtab instead as it aligns with some linker behaviors. This patch adds a buffer to save all the contents in a single place for SHA-1 calculation. Probably we need to add sha1_update() or similar to update the existing hash value with different contents and use it here. But it's out of scope for this change and I'd like something that can be backported to the stable trees easily. Reviewed-by: Ian Rogers Cc: Eric Biggers Cc: Pablo Galindo Cc: Fangrui Song Link: https://github.com/python/cpython/issues/139544 Fixes: e3f612c1d8f3945b ("perf genelf: Remove libcrypto dependency and use built-in sha1()") Signed-off-by: Namhyung Kim

perf genelf: Fix NO_LIBDW=1 build

2025-07-03T02:01:54Z

With NO_LIBDW=1 a new unused-parameter warning/error has appeared: ``` util/genelf.c: In function ‘jit_write_elf’: util/genelf.c:163:32: error: unused parameter ‘load_addr’ [-Werror=unused-parameter] 163 | jit_write_elf(int fd, uint64_t load_addr, const char *sym, ``` Fixes: e3f612c1d8f3 ("perf genelf: Remove libcrypto dependency and use built-in sha1()") Signed-off-by: Ian Rogers Tested-by: Namhyung Kim Link: https://lore.kernel.org/r/20250702175402.761818-1-irogers@google.com Signed-off-by: Namhyung Kim

perf genelf: Remove libcrypto dependency and use built-in sha1()

2025-06-26T17:51:40Z

genelf is the only file in perf that depends on libcrypto (or openssl) which only calculates a Build ID (SHA1, MD5, or URANDOM). SHA1 was expected to be the default option, but MD5 was used by default due to previous issues when linking against Java. This commit switches genelf to use the in-house sha1(), and also removes MD5 and URANDOM options since we have a reliable SHA1 implementation to rely on. It passes the tools/perf/tests/shell/test_java_symbol.sh test. Signed-off-by: Yuzhuo Jing Co-developed-by: Eric Biggers Signed-off-by: Eric Biggers Reviewed-by: Ian Rogers Link: https://lore.kernel.org/r/20250625202311.23244-4-ebiggers@kernel.org Signed-off-by: Namhyung Kim

perf build: Rename HAVE_DWARF_SUPPORT to HAVE_LIBDW_SUPPORT

2024-10-18T17:17:40Z

In Makefile.config for unwinding the name dwarf implies either libunwind or libdw. Make it clearer that HAVE_DWARF_SUPPORT is really just defined when libdw is present by renaming to HAVE_LIBDW_SUPPORT. Signed-off-by: Ian Rogers Acked-by: Namhyung Kim Tested-by: Leo Yan Cc: Anup Patel Cc: Yang Jihong Cc: Palmer Dabbelt Cc: David S. Miller Cc: Albert Ou Cc: Shenlin Liang Cc: Nick Terrell Cc: Guilherme Amadio Cc: Steinar H. Gunderson Cc: Changbin Du Cc: Alexander Lobakin Cc: Przemek Kitszel Cc: Huacai Chen Cc: Guo Ren Cc: Masahiro Yamada Cc: Masami Hiramatsu (Google) Cc: Will Deacon Cc: James Clark Cc: Mike Leach Cc: Chen Pei Cc: Leo Yan Cc: Oliver Upton Cc: Aditya Gupta Cc: Kajol Jain Cc: Athira Rajeev Cc: linux-arm-kernel@lists.infradead.org Cc: linux-riscv@lists.infradead.org Cc: Bibo Mao Cc: John Garry Cc: Atish Patra Cc: Dima Kogan Cc: Paul Walmsley Cc: Dr. David Alan Gilbert Cc: linux-csky@vger.kernel.org Link: https://lore.kernel.org/r/20241017001354.56973-11-irogers@google.com Signed-off-by: Namhyung Kim

perf genelf: remove unused struct 'options'

2024-06-04T05:07:52Z

'options' has been unused since commit fa7f7e735495 ("perf jit: Move test functionality in to a test"). Remove it. Signed-off-by: Dr. David Alan Gilbert Reviewed-by: Ian Rogers Signed-off-by: Namhyung Kim Link: https://lore.kernel.org/r/20240602000505.213032-1-linux@treblig.org

perf genelf: Set ELF program header addresses properly

2023-12-14T21:56:34Z

The text section starts after the ELF headers so PHDR.p_vaddr and others should have the correct addresses. Fixes: babd04386b1df8c3 ("perf jit: Include program header in ELF files") Reviewed-by: Ian Rogers Signed-off-by: Namhyung Kim Cc: Adrian Hunter Cc: Fangrui Song Cc: Ingo Molnar Cc: Jiri Olsa Cc: Lieven Hey Cc: Milian Wolff Cc: Pablo Galindo Cc: Peter Zijlstra Link: https://lore.kernel.org/r/20231212070547.612536-2-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo

perf genelf: Fix error code in jit_write_elf()

2022-10-04T11:55:22Z

The error code is set to -1 at the beginning of jit_write_elf(), but it is assigned by jit_add_eh_frame_info() in the middle, hence the following error can only return the error code of jit_add_eh_frame_info(). Reset the error code to the default value after being assigned by jit_add_eh_frame_info(). Fixes: 086f9f3d7897d808 ("perf jit: Generate .eh_frame/.eh_frame_hdr in DSO") Signed-off-by: Shang XiaoJing Cc: Alexander Shishkin Cc: Ingo Molnar Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stefano Sanfilippo Link: https://lore.kernel.org/r/20220922141438.22487-2-shangxiaojing@huawei.com Signed-off-by: Arnaldo Carvalho de Melo

perf jit: Include program header in ELF files

2022-09-21T13:30:55Z

The missing header makes it hard for programs like elfutils to open these files. Fixes: 2d86612aacb7805f ("perf symbol: Correct address for bss symbols") Reviewed-by: Leo Yan Signed-off-by: Lieven Hey Tested-by: Leo Yan Cc: Leo Yan Link: https://lore.kernel.org/r/20220915092910.711036-1-lieven.hey@kdab.com Signed-off-by: Arnaldo Carvalho de Melo

perf genelf: Switch deprecated openssl MD5_* functions to new EVP API

2022-09-06T12:45:23Z

Switch to the flavored EVP API like in test-libcrypto.c, and remove the bad gcc #pragma. Inspired-by: 5b245985a6de5ac1 ("tools build: Switch to new openssl API for test-libcrypto") Signed-off-by: Zixuan Tan Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Link: http://lore.kernel.org/lkml/CABwm_eTnARC1GwMD-JF176k8WXU1Z0+H190mvXn61yr369qt6g@mail.gmail.com Signed-off-by: Arnaldo Carvalho de Melo