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From: Simon Marchi <simark@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] gdb: fix undefined behavior reported in copy_bitwise Date: Sat, 11 Apr 2020 01:07:05 +0000 (GMT) [thread overview] Message-ID: <20200411010706.01D34385B835@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=cf83625da29d1239e97f1eb4d145f347cb741889 commit cf83625da29d1239e97f1eb4d145f347cb741889 Author: Artur Shepilko <nomadbyte@gmail.com> Date: Fri Apr 10 10:56:43 2020 -0400 gdb: fix undefined behavior reported in copy_bitwise gdb version 9.1, built with clang 8.0.0 on Ubuntu 18.04 (x86_64); --enable-ubsan (for clang's undefined behavior sanitizer) Executing command; `maint selftest copy_bitwise` bombs in runtime error: ../../gdb/utils.c:3432:28: runtime error: left shift of negative value -1 Closer look reveals the offending shift: `(~0 << nbits)`, apparently 0 is treated as signed int, resulting in negative complement. Explicitly stating it unsigned 0U fixes it and the `copy_bitwise` test passes ok. Diff: --- gdb/ChangeLog | 5 +++++ gdb/utils.c | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 661a41467bb..81102ee569b 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2020-04-10 Artur Shepilko <nomadbyte@gmail.com> + + * utils.c (copy_bitwise): Use unsigned 0 constant as operand of + bit shift. + 2020-04-10 Tom Tromey <tromey@adacore.com> * symfile.c (symbol_file_add_separate): Preserve OBJF_MAINLINE. diff --git a/gdb/utils.c b/gdb/utils.c index bda6bbf5b0e..f5b20331b1e 100644 --- a/gdb/utils.c +++ b/gdb/utils.c @@ -3433,7 +3433,7 @@ copy_bitwise (gdb_byte *dest, ULONGEST dest_offset, buf |= *source << avail; buf &= (1 << nbits) - 1; - *dest = (*dest & (~0 << nbits)) | buf; + *dest = (*dest & (~0U << nbits)) | buf; } }
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