[PATCH V5] PowerPC: fix for gdb.base/eh_return.exp

[Carl Love]

Will, Pedro, Kevin, GDB maintainers:

Oops, accidentally hit send.  Didn't get the patch attached yet.

I have made the additional fixes to the comments and the setting of the
clang options as mentioned by Will in version 4.  I do not have an
environment where gdb can be built with clang.  But I did check that
the clang options are properly passed to the compile command. 
Unfortunately, extensive testing of gdb built with XLC and clang are
beyond the scope of this patch as I do not have access to such systems.

Per the comments from Kevin, the patch was updated to check for the gcc
and xlc compilers on PowerPC.  The patch was also tested and verified
on AIX which uses the gcc compiler to build gdb.  The attempt to build
gdb using the xlc compiler fails due to unrelated compiler errors.  The
xlc options to disable the Traceback Table was verified but that was
it.

I have updated the patch per the comments from Will.  The new version
of the patch uses a PowerPC specific gcc option to suppress the
generation of the Traceback Table information.  The Traceback
information for this function is contained in the .long statements
following the last instruction in the function.  The Traceback table
consists of a series of bit fields.  The assembler tries to interpret
the Traceback Table as instructions.  If the bits in the Traceback
Table happen to match a known instruction, the assembler will print a
bogus instruction, otherwise the assembler just prints the bits using
the .long statement.  Unfortunately, the disassembler does not know how
to locate the Traceback Table information at the end of a function.

With this patch, the Traceback Table is disabled, so the last
instruction of the function is accurately found.  Previously, the break
point was set at the last .long statement which gdb will never reach. 
The test now passes as gdb successfully executes to the identified last
instruction.

Note, the use of the gcc mtraceback option is not valid on other
architectures.

I have tested the patch on Linux Power 10 with gcc, AIX with the gcc
and Intel with gcc.

Please let me know if this patch is acceptable.  Thanks for the input
and help with the patch.

                          Carl Love

------------------------------------------------------------------

PowerPC: fix for gdb.base/eh_return.exp

Disable the Traceback Table generation on PowerPC for this test.  The
Traceback Table consists of a series of bit fields to indicate things like
the Traceback Table version, language, and specific information about the
function.  The Traceback Table is generated following the end of the code
for every function by default.  The Traceback Table is defined in the
PowerPC ELF ABI and is intended to support debuggers and exception
handlers.  The Traceback Table is displayed in the disassembly of functions
by default and is part of the function length.  The table is typically
interpreted by the disassembler as data represented by .long xxx entries.

Generation of the Traceback Table is disabled in this test using the
PowerPC specific gcc compiler option -mtraceback=no, the xlc option
additional_flags-qtable=none and the clang optons
 -mllvm -xcoff-traceback-table=false.  Disabling the Traceback Table
generation in this test results in the gdb_test_multiple statement
correctly locating the address of the bclr instruction before the statement
"End of assembler dump." in the disassembly output.
---
 gdb/testsuite/gdb.base/eh_return.exp | 36 +++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.base/eh_return.exp b/gdb/testsuite/gdb.base/eh_return.exp
index df55dbc72da..6e4b9bd0bba 100644
--- a/gdb/testsuite/gdb.base/eh_return.exp
+++ b/gdb/testsuite/gdb.base/eh_return.exp
@@ -18,8 +18,42 @@
 
 standard_testfile
 
+# Set compiler flags.
+if {[istarget "powerpc*"]} then {
+    # PowerPC generates a Traceback Table, as defined in the PPC64 ABI,
+    # following each function by default.  The Traceback Table information is
+    # typically interpreted by the disassembler as data represented with
+    # .long xxxx following the last instruction in the function.  For example:
+    #
+    #   Dump of assembler code for function eh2:
+    #   0x00000000100009e0 <+0>:     lis     r2,4098
+    #   ...
+    #   0x0000000010000b04 <+292>:   add     r1,r1,r10
+    #   0x0000000010000b08 <+296>:   blr
+    #   0x0000000010000b0c <+300>:   .long 0x0
+    #   0x0000000010000b10 <+304>:   .long 0x1000000
+    #   0x0000000010000b14 <+308>:   .long 0x1000180
+    #   End of assembler dump.
+    #
+    # Disable the Traceback Table generation, using the PowerPC specific
+    # compiler option, so the test gdb_test_multiple "disassemble eh2" will
+    # locate the address of the blr instruction not the last .long statement.
+    if { [test_compiler_info "gcc-*"] } {
+	set compile_flags {debug nopie additional_flags=-mtraceback=no}
+    } elseif { [test_compiler_info "xlc-*"] } {
+	set compile_flags {debug nopie additional_flags=-qtbtable=none}
+    } elseif { [test_compiler_info "clang-*"] } {
+	set compile_flags [list debug nopie additional_flags=-mllvm \
+			       additional_flags=-xcoff-traceback-table=false]
+    } else {
+	set compile_flags {debug nopie }
+    }
+} else {
+    set compile_flags {debug nopie}
+}
+
 if {[prepare_for_testing "failed to prepare" $testfile $srcfile \
-	 {debug nopie}]} {
+	 $compile_flags]} {
     return -1
 }
 
-- 
2.31.1