[PATCH 1/7] gdb: recognize 64 bits Windows executables as Cygwin osabi

Simon Marchi
2020-03-16T17:08:49Z

From: Simon Marchi <simon.marchi@efficios.com>

If I generate two Windows PE executables, one 32 bits and one 64 bits:

$ x86_64-w64-mingw32-gcc test.c -g3 -O0 -o test_64
$ i686-w64-mingw32-gcc test.c -g3 -O0 -o test_32
$ file test_64
test_64: PE32+ executable (console) x86-64, for MS Windows
$ file test_32
test_32: PE32 executable (console) Intel 80386, for MS Windows

When I load the 32 bits binary in my GNU/Linux-hosted GDB, the osabi is
correctly recognized as "Cygwin":

$ ./gdb --data-directory=data-directory -nx test_32
(gdb) show osabi
The current OS ABI is "auto" (currently "Cygwin").

When I load the 64 bits binary in GDB, the osabi is incorrectly
recognized as "GNU/Linux":

$ ./gdb --data-directory=data-directory -nx test_64
(gdb) show osabi
The current OS ABI is "auto" (currently "GNU/Linux").

The 32 bits one gets recognized by the i386_cygwin_osabi_sniffer
function, by its target name:

if (strcmp (target_name, "pei-i386") == 0)
return GDB_OSABI_CYGWIN;

The target name for the 64 bits binaries is "pei-x86-64". It doesn't
get recognized by any osabi sniffer, so GDB falls back on its default
osabi, "GNU/Linux".

This patch adds an osabi sniffer function for the Windows 64 bits
executables in amd64-windows-tdep.c. With it, the osabi is recognized
as "Cygwin", just like with the 32 bits binary.

Note that it may seems strange to have a binary generated by MinGW
(which has nothing to do with Cygwin) be recognized as a Cygwin binary.
This is indeed not accurate, but at the moment GDB uses the Cygwin for
everything Windows. Subsequent patches will add a separate "Windows" OS
ABI for Windows binaries that are not Cygwin binaries.

gdb/ChangeLog:

* amd64-windows-tdep.c (amd64_windows_osabi_sniffer): New
function.
(_initialize_amd64_windows_tdep): Register osabi sniffer.
---
gdb/amd64-windows-tdep.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/gdb/amd64-windows-tdep.c b/gdb/amd64-windows-tdep.c
index d4d79682dd18..2ca979513cd7 100644
--- a/gdb/amd64-windows-tdep.c
+++ b/gdb/amd64-windows-tdep.c
@@ -1244,10 +1244,24 @@ amd64_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
set_gdbarch_auto_wide_charset (gdbarch, amd64_windows_auto_wide_charset);
}

+static gdb_osabi
+amd64_windows_osabi_sniffer (bfd *abfd)
+{
+ const char *target_name = bfd_get_target (abfd);
+
+ if (strcmp (target_name, "pei-x86-64") == 0)
+ return GDB_OSABI_CYGWIN;
+
+ return GDB_OSABI_UNKNOWN;
+}
+
void _initialize_amd64_windows_tdep ();
void
_initialize_amd64_windows_tdep ()
{
gdbarch_register_osabi (bfd_arch_i386, bfd_mach_x86_64, GDB_OSABI_CYGWIN,
amd64_windows_init_abi);
+
+ gdbarch_register_osabi_sniffer (bfd_arch_i386, bfd_target_coff_flavour,
+ amd64_windows_osabi_sniffer);
}
--
2.25.1