[binutils-gdb] readelf: invalid error message triggered when last tag is an empty string

[Matthieu Longo]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=86a053ddd1e2534c588d8d6f56752fb51dd1b184

commit 86a053ddd1e2534c588d8d6f56752fb51dd1b184
Author: Matthieu Longo <matthieu.longo@arm.com>
Date:   Thu Apr 17 09:11:24 2025 +0100

    readelf: invalid error message triggered when last tag is an empty string
    
    Disclaimer: this issue cannot occur with Object Attributes v1 (OAv1) while
    using the GNU binutils because a value of '\0' (empty string) for a tag
    with a string value is considered as the default value for the attribute,
    and consequently is eliminated by gas from the output object file during
    the serialization.
    
    An empty string is a valid value for a NTBS tag in both OAv1 and OAv2 [1]
    cases. However, contrarily to OAv1, a OAv2 subsection can be required and
    so, tags in this subsection might have to be present even if the value is
    the default. To comply with this requirement, the OAv2 serializer won't
    drop the default values.
    
    In the case where a NTBS tag has the value '\0' and is last in the object
    attributes section, the current code in readelf used for dumping the object
    attributes incorrectly detects an overflow, and prints out an error message
    for a corrupted string tag.
    
    This patch fixes the detection of the overflow so that it now accept an
    empty string in the last tag of the object attributes section.
    
    It also fixes the previous tests for the empty NTBS case and the non-null
    terminated string one. The fix was also tested in the context of OAv2's
    patch series [1] where the issue was originally detected. No regression
    was found.
    
    [1]: https://inbox.sourceware.org/binutils/20250509151319.88725-1-matthieu
         .longo@arm.com/

Diff:
---
 binutils/readelf.c                                      | 8 ++++++--
 gas/testsuite/gas/arm/attr-empty-string.d               | 1 -
 gas/testsuite/gas/arm/attr-non-null-terminated-string.d | 2 +-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/binutils/readelf.c b/binutils/readelf.c
index 77a88bff032..f49092f11b9 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -17779,13 +17779,17 @@ display_tag_value (signed int tag,
   else if (tag & 1)
     {
       /* PR 17531 file: 027-19978-0.004.  */
-      size_t maxlen = (end - p) - 1;
+      size_t maxlen = end - p;
 
       putchar ('"');
       if (maxlen > 0)
 	{
+	  maxlen -= 1; /* Remove \0 from the character count.  */
 	  print_symbol_name ((int) maxlen, (const char *) p);
-	  p += strnlen ((char *) p, maxlen) + 1;
+	  size_t len = strnlen ((char *) p, maxlen);
+	  if (len == maxlen && p[maxlen] != '\0')
+	    printf (_("<corrupt string tag>"));
+	  p += len + 1;
 	}
       else
 	{
diff --git a/gas/testsuite/gas/arm/attr-empty-string.d b/gas/testsuite/gas/arm/attr-empty-string.d
index 3c6560c80a8..b4a91418e80 100644
--- a/gas/testsuite/gas/arm/attr-empty-string.d
+++ b/gas/testsuite/gas/arm/attr-empty-string.d
@@ -4,7 +4,6 @@
 # readelf: -T -A
 # This test is only valid on EABI based ports.
 # target: *-*-*eabi* *-*-nacl*
-# xfail: *
 
 Attribute Section: aeabi
 File Attributes
diff --git a/gas/testsuite/gas/arm/attr-non-null-terminated-string.d b/gas/testsuite/gas/arm/attr-non-null-terminated-string.d
index d079d14903e..ac376a9ab9f 100644
--- a/gas/testsuite/gas/arm/attr-non-null-terminated-string.d
+++ b/gas/testsuite/gas/arm/attr-non-null-terminated-string.d
@@ -6,4 +6,4 @@
 # readelf: --silent-truncation -A
 Attribute Section: aeabi
 File Attributes
-  Tag_CPU_raw_name: "ab"
+  Tag_CPU_raw_name: "ab<corrupt string tag>"