sorttable: parse nm output correctly

sorttable reads a list of functions from vmlinux, provided by the output of
nm, with the -S flag specified providing function sizes.

It does so using fscanf(fp, "%16s %16s %c %*s\n", ...) reading address,
size, type (a single character) and name.

However, nm outputs no size for a symbol which has none, meaning that it
misinterprets these entries - interpreting the type character as the size,
and, if the name is a single character, ignores the newline and swallows
the address of the next entry.

Size-less single character names exist (e.g. the assemblers' loop counters
left over as local absolute symbols):

      0000000000000001 a i
      000000000000000f a i
      0000000000000050 a j
      0000000000000052 a t
      000000000000009f a i
      0000000000000200 a i

sorttable is looking for functions and these are not that, and with nm's
output sorted, it just so happens to be that what's swallowed is never a
function.

However the next commit in this series stops sorting nm's output, so this
bug can results in function names being lost.

Fix the issue by using '%*[^\n]' in fscanf() rather than '%*s' such that
the scan cannot move past the newline.

Then, compare the address and size fields (which are always padded to the
same width if output by nm) - if they differ, then this is a misread, so
simply discard the entry.

It's fine to discard these, as sorttable's raison d'être is to discover
whether a call site is contained within a function and an empty function
can't contain anything.

Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Link: https://patch.msgid.link/20260923-build-speedup-v4-4-73128809a4a4@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

0 files changed, 0 insertions, 0 deletions