[gdb/testsuite] Fix gdb.base/step-over-syscall.exp with -m32

When executing test-case gdb.base/step-over-syscall.exp with target board
unix/-m32, we run into:
...
(gdb) x/2i $pc^M
=> 0xf7fd5155 <__kernel_vsyscall+5>:    sysenter ^M
   0xf7fd5157 <__kernel_vsyscall+7>:    int    $0x80^M
(gdb) PASS: gdb.base/step-over-syscall.exp: fork: displaced=off: \
  pc before/after syscall instruction
stepi^M
[Detaching after fork from child process 23593]^M
0xf7fd5159 in __kernel_vsyscall ()^M
1: x/i $pc^M
=> 0xf7fd5159 <__kernel_vsyscall+9>:    pop    %ebp^M
(gdb) PASS: gdb.base/step-over-syscall.exp: fork: displaced=off: stepi fork insn
print /x $pc^M
$2 = 0xf7fd5159^M
(gdb) PASS: gdb.base/step-over-syscall.exp: fork: displaced=off: pc after stepi
FAIL: gdb.base/step-over-syscall.exp: fork: displaced=off: \
  pc after stepi matches insn addr after syscall
...

The test tries to verify that after doing a stepi at a syscall insn, the $pc
is matching the insn after the syscall insn.

However, in the case that the syscall insn is "sysenter", the stepi will land
further away, so in this case:
...
   0xf7fd5155 <__kernel_vsyscall+5>:    sysenter ^M
   0xf7fd5157 <__kernel_vsyscall+7>:    int    $0x80^M
   0xf7fd5159 <__kernel_vsyscall+9>:    pop    %ebp^M
...
the stepi will land at 0xf7fd5159 instead of 0xf7fd5157.

Fix this by detecting the sysenter/int sequence and adjusting the expected
pc.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-01-19  Tom de Vries  <tdevries@suse.de>

	* gdb.base/step-over-syscall.exp: Detect and handle sysenter/int
	sequence.

2 files changed, 28 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 9bb70f7..f6f0274 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2021-01-19  Tom de Vries  <tdevries@suse.de>
 
+	* gdb.base/step-over-syscall.exp: Detect and handle sysenter/int
+	sequence.
+
+2021-01-19  Tom de Vries  <tdevries@suse.de>
+
 	* gdb.arch/i386-mpx.c (main): Drop argc/argv parameter.
 
 2021-01-18  Andrew Burgess  <andrew.burgess@embecosm.com>
diff --git a/gdb/testsuite/gdb.base/step-over-syscall.exp b/gdb/testsuite/gdb.base/step-over-syscall.exp
index e6f58ae..ecfb7be 100644
--- a/gdb/testsuite/gdb.base/step-over-syscall.exp
+++ b/gdb/testsuite/gdb.base/step-over-syscall.exp
@@ -155,11 +155,34 @@ proc setup { syscall } {
     gdb_test_multiple "x/2i \$pc" "pc before/after syscall instruction" {
 	-re "x/2i .*=> ($hex) .*:.*$syscall_insn.* ($hex) .*:.*$gdb_prompt $" {
 	    set syscall_insn_addr $expect_out(1,string)
+	    set actual_syscall_insn $expect_out(2,string)
 	    set next_insn_addr $expect_out(3,string)
 	    pass $gdb_test_name
 	}
     }
 
+    # If we encounter a sequence:
+    #   0xf7fd5155 <__kernel_vsyscall+5>:    sysenter
+    #   0xf7fd5157 <__kernel_vsyscall+7>:    int    $0x80
+    #   0xf7fd5159 <__kernel_vsyscall+9>:    pop    %ebp
+    # then a stepi at sysenter will step over the int insn, so make sure
+    # next_insn_addr points after the int insn.
+    if { $actual_syscall_insn == "sysenter" } {
+	set test "pc after sysenter instruction"
+	set re_int_insn "\[ \t\]*int\[ \t\]\[^\r\n\]*"
+	set re [multi_line \
+		    "x/2i $hex" \
+		    "\[^\r\n\]* $hex \[^\r\n\]*:$re_int_insn" \
+		    "\[^\r\n\]* ($hex) \[^\r\n\]*:\[^\r\n\]*"]
+	gdb_test_multiple "x/2i $next_insn_addr" $test {
+	    -re -wrap $re {
+		set next_insn_addr $expect_out(1,string)
+	    }
+	    -re -wrap "" {
+	    }
+	}
+    }
+
     if {[gdb_test "stepi" "x/i .*=>.*" "stepi $syscall insn"] != 0} {
 	return { -1, -1 }
     }