[binutils-gdb] [gdb/testsuite] Fix race in gdb.base/add-symbol-file-attach.exp

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1b9a9c30a073c9be8ae12faf195021e843ba9757

commit 1b9a9c30a073c9be8ae12faf195021e843ba9757
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Sep 4 13:54:36 2023 +0200

    [gdb/testsuite] Fix race in gdb.base/add-symbol-file-attach.exp
    
    When running test-case gdb.base/add-symbol-file-attach.exp with target board
    unix/-m32, we run into:
    ...
    (gdb) attach 3955^M
    Attaching to process 3955^M
    Load new symbol table from "add-symbol-file-attach"? (y or n) y^M
    Reading symbols from add-symbol-file-attach/add-symbol-file-attach...^M
    Reading symbols from /lib/libm.so.6...^M
    Reading symbols from /usr/lib/debug/lib/libm-2.31.so-i386.debug...^M
    Reading symbols from /lib/libc.so.6...^M
    Reading symbols from /usr/lib/debug/lib/libc-2.31.so-i386.debug...^M
    Reading symbols from /lib/ld-linux.so.2...^M
    Reading symbols from /usr/lib/debug/lib/ld-2.31.so-i386.debug...^M
    0xf7f53549 in __kernel_vsyscall ()^M
    (gdb) FAIL: gdb.base/add-symbol-file-attach.exp: attach
    ...
    
    The test fails because this regexp is used:
    ...
        -re ".*in \[_A-Za-z0-9\]*pause.*$gdb_prompt $" {
    ...
    
    The regexp attempts to detect that the exec is somewhere in pause ():
    ...
    int
    main (int argc, char **argv)
    {
      pause ();
      return 0;
    }
    ...
    but when the exec is blocked in pause, the backtrace is:
    ...
     (gdb) bt
     #0  0xf7fd2549 in __kernel_vsyscall ()
     #1  0xf7d84966 in __libc_pause () at ../sysdeps/unix/sysv/linux/pause.c:29
     #2  0x0804844c in main (argc=1, argv=0xffffce84)
         at /data/vries/gdb/src/gdb/testsuite/gdb.base/add-symbol-file-attach.c:26
    ...
    
    We could simply extend the regexp to also match __kernel_vsyscall, but the
    more fundamental problem is that the test is racy.
    
    The attach can happen before the exec is blocked in pause (), somewhere in the
    dynamic linker resolving the call to pause, in main or even earlier.
    
    Note that for the test-case to be effective, the exec is not required to be in
    pause ().  I added a "while (1);" loop at the start of main, reverted the
    patch fixing the corresponding PR and reproduced the problem it's supposed to
    detect.
    
    Fix this by simply matching the "Reading symbols from" line, similar to what
    an earlier test is doing.
    
    While we're at it, rewrite the earlier test to also use the -wrap idiom.
    
    Tested on x86_64-linux.

Diff:
---
 gdb/testsuite/gdb.base/add-symbol-file-attach.exp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.base/add-symbol-file-attach.exp b/gdb/testsuite/gdb.base/add-symbol-file-attach.exp
index 373f3c400f7..bbdfd994d49 100644
--- a/gdb/testsuite/gdb.base/add-symbol-file-attach.exp
+++ b/gdb/testsuite/gdb.base/add-symbol-file-attach.exp
@@ -57,7 +57,7 @@ gdb_test_multiple "add-symbol-file $binfile" $test {
 	send_gdb "y\n"
 	exp_continue
     }
-    -re "Reading symbols from.*$gdb_prompt $" {
+    -re -wrap "Reading symbols from .*" {
 	pass $test
     }
 }
@@ -71,7 +71,7 @@ gdb_test_multiple "attach $testpid" $test {
 	send_gdb "y\n"
 	exp_continue
     }
-    -re ".*in \[_A-Za-z0-9\]*pause.*$gdb_prompt $" {
+    -re -wrap "Reading symbols from .*" {
 	pass $test
     }
 }