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[binutils-gdb] Avoid undefined behavior in extract_integer


https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=0101665f864383147448c5871a67286a3f7a9a28

commit 0101665f864383147448c5871a67286a3f7a9a28
Author: Tom Tromey <tom@tromey.com>
Date:   Sun Jul 29 17:16:03 2018 -0600

    Avoid undefined behavior in extract_integer
    
    -fsanitize=undefined showed that extract_integer could left-shift a
    negative value, which is undefined.  This patch fixes the problem by
    doing all the work in an unsigned type.  This relies on
    implementation-defined behavior, but I tend to think we are on safe
    ground there.  (Also, if need be, violations of this could probably be
    detected, either by configure or by a static_assert.)
    
    gdb/ChangeLog
    2018-10-03  Tom Tromey  <tom@tromey.com>
    
    	* findvar.c (extract_integer): Do work in an unsigned type.

Diff:
---
 gdb/ChangeLog | 4 ++++
 gdb/findvar.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 36c4493..5787d44 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,9 @@
 2018-10-03  Tom Tromey  <tom@tromey.com>
 
+	* findvar.c (extract_integer): Do work in an unsigned type.
+
+2018-10-03  Tom Tromey  <tom@tromey.com>
+
 	* common/enum-flags.h (enum_flags::operator~): Add static assert.
 	* symfile-add-flags.h (enum symfile_add_flag): Use unsigned as
 	base type.
diff --git a/gdb/findvar.c b/gdb/findvar.c
index 9256833..be6c9d6 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -50,7 +50,7 @@ template<typename T, typename>
 T
 extract_integer (const gdb_byte *addr, int len, enum bfd_endian byte_order)
 {
-  T retval = 0;
+  typename std::make_unsigned<T>::type retval = 0;
   const unsigned char *p;
   const unsigned char *startaddr = addr;
   const unsigned char *endaddr = startaddr + len;


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