[PATCH] libdwfl: Declare possible zero sized arrays only when non-zero

[Mark Wielaard]

The gcc undefined sanitizer complains when seeing a zero sized array
declaration. Move the declaration to the point in the code where we
know they aren't zero sized.

https://sourceware.org/bugzilla/show_bug.cgi?id=28720

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 libdwfl/ChangeLog  | 5 +++++
 libdwfl/link_map.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index aace969f..b2588b12 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,8 @@
+2022-01-03  Mark Wielaard  <mark@klomp.org>
+
+	* link_map.c (dwfl_link_map_report): Only declare d32 and d64 before
+	actual use.
+
 2022-01-03  Mark Wielaard  <mark@klomp.org>
 
 	* dwfl_segment_report_module.c (dwfl_segment_report_module): Copy
diff --git a/libdwfl/link_map.c b/libdwfl/link_map.c
index 99222bb9..c0207cd3 100644
--- a/libdwfl/link_map.c
+++ b/libdwfl/link_map.c
@@ -1037,8 +1037,6 @@ dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
 		  return false;
 		}
 	      void *buf = malloc (dyn_filesz);
-	      Elf32_Dyn (*d32)[dyn_filesz / sizeof (Elf32_Dyn)] = buf;
-	      Elf64_Dyn (*d64)[dyn_filesz / sizeof (Elf64_Dyn)] = buf;
 	      if (unlikely (buf == NULL))
 		{
 		  __libdwfl_seterrno (DWFL_E_NOMEM);
@@ -1068,6 +1066,7 @@ dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
 		  /* We are looking for DT_DEBUG.  */
 		  if (elfclass == ELFCLASS32)
 		    {
+		      Elf32_Dyn (*d32)[dyn_filesz / sizeof (Elf32_Dyn)] = buf;
 		      size_t n = dyn_filesz / sizeof (Elf32_Dyn);
 		      for (size_t i = 0; i < n; ++i)
 			if ((*d32)[i].d_tag == DT_DEBUG)
@@ -1078,6 +1077,7 @@ dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
 		    }
 		  else
 		    {
+		      Elf64_Dyn (*d64)[dyn_filesz / sizeof (Elf64_Dyn)] = buf;
 		      size_t n = dyn_filesz / sizeof (Elf64_Dyn);
 		      for (size_t i = 0; i < n; ++i)
 			if ((*d64)[i].d_tag == DT_DEBUG)
-- 
2.30.2