From 39f28eaf8c821d71d57ffc759655ec4168d0bead Mon Sep 17 00:00:00 2001 From: Mark Wielaard Date: Thu, 16 Apr 2020 17:45:31 +0200 Subject: [PATCH] libdwfl: Initialize bits to NULL in dwfl_standard_find_debuginfo for LTO. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit GCC10 LTO is too smart (and somewhat cryptic): find-debuginfo.c: In function ‘dwfl_standard_find_debuginfo’: debuginfod-client.c:85:8: error: ‘bits’ may be used uninitialized in this function [-Werror=maybe-uninitialized] find-debuginfo.c:360:24: note: ‘bits’ was declared here lto1: all warnings being treated as errors So it inlines __libdwfl_debuginfod_find_debuginfo into dwfl_standard_find_debuginfo and since it cannot see into the function pointer (*fp_debuginfod_find_debuginfo), it assumes that build_id_bit (== bits in dwfl_standard_find_debuginfo) will be used by the called function and it might not be initialized. But if you read the code the there is a check for build_id_len > 0 to see whether bits is or isn't initialized before using bits. But gcc isn't smart enough to figure that out. Maybe that actually should be an heuristic gcc lto should use. If the callchain I am inlining is so deep that I cannot figure out maybe-uninitialized variables anymore I should stop inlining. For now just help GCC out and initialize bits to NULL. Signed-off-by: Mark Wielaard --- libdwfl/ChangeLog | 5 +++++ libdwfl/find-debuginfo.c | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog index 0b95490aa..4ddc9ad47 100644 --- a/libdwfl/ChangeLog +++ b/libdwfl/ChangeLog @@ -1,3 +1,8 @@ +2020-04-16 Mark Wielaard + + * find-debuginfo.c (dwfl_standard_find_debuginfo): Initialize bits + to NULL. + 2020-01-24 Mark Wielaard * linux-kernel-modules.c (find_kernel_elf): Check release isn't NULL. diff --git a/libdwfl/find-debuginfo.c b/libdwfl/find-debuginfo.c index 408576454..2dd11c48d 100644 --- a/libdwfl/find-debuginfo.c +++ b/libdwfl/find-debuginfo.c @@ -357,7 +357,7 @@ dwfl_standard_find_debuginfo (Dwfl_Module *mod, { /* First try by build ID if we have one. If that succeeds or fails other than just by finding nothing, that's all we do. */ - const unsigned char *bits; + const unsigned char *bits = NULL; GElf_Addr vaddr; int bits_len; if ((bits_len = INTUSE(dwfl_module_build_id) (mod, &bits, &vaddr)) > 0) -- 2.47.3