[Valgrind-developers] [valgrind] coregrind/m_debuginfo: don't try to examine zero sized mmapped files

[Mark W. <ma...@so...>]

https://sourceware.org/git/gitweb.cgi?p=valgrind.git;h=86ac4f2b004f57fa11224efafc1cd1c8fa8ded84

commit 86ac4f2b004f57fa11224efafc1cd1c8fa8ded84
Author: Mark Wielaard <ma...@kl...>
Date:   Sun Mar 9 15:59:29 2025 +0100

    coregrind/m_debuginfo: don't try to examine zero sized mmapped files
    
    When run on an nfs filesystem memcheck/tests/pointer-trace fails
    because it generates warnings "connection to image failed". This is
    caused by trying to mmap a deleted file which the nfs file system
    represents as a (hidden) regular file. This is normally not a problem
    except when that file is empty.
    
    Fix this by not trying to check whether a file is an ELF or MACHO
    against an empty (regular) file in di_notify_mmap. An empty file is
    never a valid ELF or MACHO file (and cannot be represented as
    DiImage).
    
    https://bugs.kde.org/show_bug.cgi?id=501119

Diff:
---
 NEWS                              |  1 +
 coregrind/m_debuginfo/debuginfo.c | 10 ++++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/NEWS b/NEWS
index 0fcbc5d0e2..16cfeef2a4 100644
--- a/NEWS
+++ b/NEWS
@@ -56,6 +56,7 @@ are not entered into bugzilla tend to get forgotten about or ignored.
 498492  none/tests/amd64/lzcnt64 crashes on FreeBSD compiled with clang
 499183  FreeBSD: differences in avx-vmovq output
 499212  mmap() with MAP_ALIGNED() returns unaligned pointer
+501119  memcheck/tests/pointer-trace fails when run on NFS filesystem
 501194  Fix ML_(check_macho_and_get_rw_loads) so that it is correct for any number of segment commands
 
 
diff --git a/coregrind/m_debuginfo/debuginfo.c b/coregrind/m_debuginfo/debuginfo.c
index 612833a997..15686fc5c4 100644
--- a/coregrind/m_debuginfo/debuginfo.c
+++ b/coregrind/m_debuginfo/debuginfo.c
@@ -1206,8 +1206,14 @@ ULong VG_(di_notify_mmap)( Addr a, Bool allow_SkFileV, Int use_fd )
    }
 
    /* Finally, the point of all this stattery: if it's not a regular file,
-      don't try to read debug info from it. */
-   if (! VKI_S_ISREG(statbuf.mode))
+      don't try to read debug info from it. Also if it is a "regular file"
+      but has a zero size then skip it. Having a zero size will definitely
+      fail when trying to create an DiImage and wouldn't be a valid elf or
+      macho file. This can happen when mmapping a deleted file, which
+      would normally fail in the check above, because the stat call will
+      fail.  But if the deleted file is on an NFS file system then a fake
+      (regular) empty file might be returned.  */
+   if (! VKI_S_ISREG(statbuf.mode) || statbuf.size == 0)
       return 0;
 
    /* no uses of statbuf below here. */