[COMMITTED] nm: Simplify naming of invalid sections, check shdr isn't NULL.

[Mark Wielaard]

When shdr is NULL or the sh_name index is invalid, don't try to use
it.  Just call the section "[invalid section name]". Don't try to be
too smart by creating a dynamic invalid name using alloca to simplify
memory usage in this exceptional case.

Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 src/ChangeLog |  5 +++++
 src/nm.c      | 14 ++++++--------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 3786f3432..3020bd768 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2019-04-28  Mark Wielaard  <m...@klomp.org>
+
+       * nm.c (show_symbols_sysv): Check gelf_getshdr doesn't return
+       NULL. Simplify naming of invalid sections, don't use alloca.
+
 2019-04-28  Mark Wielaard  <m...@klomp.org>
 
        * elfcmp.c (main): Check shdr1 and shdr2 are not NULL.
diff --git a/src/nm.c b/src/nm.c
index ffe8ca691..da1350b4c 100644
--- a/src/nm.c
+++ b/src/nm.c
@@ -751,19 +751,17 @@ show_symbols_sysv (Ebl *ebl, GElf_Word strndx, const char 
*fullname,
   while ((scn = elf_nextscn (ebl->elf, scn)) != NULL)
     {
       GElf_Shdr shdr_mem;
+      GElf_Shdr *shdr;
 
       assert (elf_ndxscn (scn) == cnt);
       cnt++;
 
-      char *name = elf_strptr (ebl->elf, shstrndx,
-                              gelf_getshdr (scn, &shdr_mem)->sh_name);
+      char *name = NULL;
+      shdr = gelf_getshdr (scn, &shdr_mem);
+      if (shdr != NULL)
+       name = elf_strptr (ebl->elf, shstrndx, shdr->sh_name);
       if (unlikely (name == NULL))
-       {
-         const size_t bufsz = sizeof "[invalid sh_name 0x12345678]";
-         name = alloca (bufsz);
-         snprintf (name, bufsz, "[invalid sh_name %#" PRIx32 "]",
-                   gelf_getshdr (scn, &shdr_mem)->sh_name);
-       }
+       name = "[invalid section name]";
       scnnames[elf_ndxscn (scn)] = name;
     }
 
-- 
2.20.1