On 08/22/2018 10:09 PM, Iain Sandoe wrote:
> Hi Tom, Richi,
>
> This is something I was experimenting with to try and solve platform problems
> with early debug.
>
> Not a “finished patch”
Hmm, not a building patch either.
> (I’ve removed the Darwin back-end parts) but would like your comments on the
> central idea.
>
> This is to switch to the alternate LTO file (this process already exists for
> the actual LTO output)
It took me a while to realize that you're talking about darwin here,
specifically the lto_start/end hooks.
> before the early debug is started and switch back to the regular output file
> after. Therefore both the LTO early debug and the LTO streamed data end up
> in a separate file (this can be concatenated as we do now, guaranteeing that
> it appears after any referenced symbols, or could be handled in “some other
> way” if that was a useful solution).
>
> Now the second part of this delays the output of the .file directives until
> the “regular” output of the asm (it could be that this could be simplified
> now there there’s a start/end function pair).
>
> The idea is that the main output text is identical with/without the early
> debug (and, in fact, it’s broken without this change - since the .file
> directives would end up in the separate LTO stream).
>
> thoughts?
> Iain
>
I found it hard to understand the above with something concrete to look
at. So I've written attach patch (targeted for my regular x86_64 linux
development platform) that adds comments in the assembly when
transitioning from one generation phase to another.
So, the effect of the patch on vla-1.c -flto -g is:
...
$ diff -I '\.section' -I '\.byte' -u 1 2
--- 1 2018-08-23 12:24:37.426659159 +0200
+++ 2 2018-08-23 12:26:46.886658665 +0200
@@ -1,6 +1,6 @@
.file "vla-1.c"
+# LTO_START
# DWARF2OUT_EARLY_FINISH START
- .file 1
"/home/vries/gcc_versions/devel/src/gcc/testsuite/gcc.dg/guality/vla-1.c"
.section .gnu.debuglto_.debug_info,"e",@progbits
.Ldebug_info0:
.hidden vla_1.c.1d3f9cc3
@@ -330,15 +330,8 @@
.byte 0
.byte 0
.byte 0x1
- .ascii
"/home/vries/gcc_versions/devel/src/gcc/testsuite/gcc.dg/gual"
- .ascii "ity"
.byte 0
.byte 0
- .string "vla-1.c"
- .uleb128 0x1
- .uleb128 0
- .uleb128 0
- .byte 0
.LELTP0:
.LELT0:
.section .gnu.debuglto_.debug_str,"eMS",@progbits,1
@@ -358,8 +351,9 @@
.string
"/home/vries/gcc_versions/devel/src/gcc/testsuite/gcc.dg/guality/vla-1.c"
.text
# DWARF2OUT_EARLY_FINISH END
+# LTO_END
# LTO_START
- .section .gnu.lto_.profile.b9a985e7cc2d09b4,"e",@progbits
+ .section .gnu.lto_.profile.922c9ad53427823c,"e",@progbits
.string "x\234\343````\004b\006"
.string ""
.string "V"
@@ -635,6 +629,7 @@
.type bar, @function
bar:
.LFB0:
+ .file 1
"/home/vries/gcc_versions/devel/src/gcc/testsuite/gcc.dg/guality/vla-1.c"
.loc 1 7 1
.cfi_startproc
.LVL0:
...
So, emitting the dwarf2 .file ALAP looks ok to me, and I think that can
be a separate patch. I wonder though if you really need a separate state
variable delay_emit_file to track this, and if you can't use
early_dwarf/early_dwarf_finished.
As for adding lto_start/end around dwarf2out_early_finish, the lto_start
hook is defined as:
...
Output to asm_out_file any text which the assembler expects to find at
the start of an LTO section.
...
Looking at the current implementation of this hook, adding this new call
pair shouldn't hurt, but perhaps we want to clarify in the documentation
that the "LTO section" can also be a debug LTO section?
Thanks,
- Tom
Add comments in .s file describing generation phases
---
gcc/dwarf2out.c | 13 ++++++++++++-
gcc/hooks.c | 15 +++++++++++++++
gcc/hooks.h | 2 ++
gcc/target.def | 4 ++--
4 files changed, 31 insertions(+), 3 deletions(-)
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index fb71ff349fa..334f9a3a901 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -31114,6 +31114,7 @@ reset_dies (dw_die_ref die)
static void
dwarf2out_finish (const char *filename)
{
+ fprintf (asm_out_file, "%s DWARF2OUT_FINISH START\n", ASM_COMMENT_START);
comdat_type_node *ctnode;
dw_die_ref main_comp_unit_die;
unsigned char checksum[16];
@@ -31565,6 +31566,7 @@ dwarf2out_finish (const char *filename)
symview_upper_bound = 0;
if (zero_view_p)
bitmap_clear (zero_view_p);
+ fprintf (asm_out_file, "%s DWARF2OUT_FINISH END\n", ASM_COMMENT_START);
}
/* Returns a hash value for X (which really is a variable_value_struct). */
@@ -31845,6 +31847,8 @@ note_variable_value (dw_die_ref die)
static void
dwarf2out_early_finish (const char *filename)
{
+ fprintf (asm_out_file, "%s DWARF2OUT_EARLY_FINISH START\n",
+ ASM_COMMENT_START);
set_early_dwarf s;
char dl_section_ref[MAX_ARTIFICIAL_LABEL_BYTES];
@@ -31899,6 +31903,8 @@ dwarf2out_early_finish (const char *filename)
fprintf (dump_file, "LTO EARLY DWARF for %s\n", filename);
print_die (comp_unit_die (), dump_file);
}
+ fprintf (asm_out_file, "%s DWARF2OUT_EARLY_FINISH END\n",
+ ASM_COMMENT_START);
return;
}
@@ -31988,7 +31994,11 @@ dwarf2out_early_finish (const char *filename)
copy_lto_debug_sections operation of the simple object support in
libiberty is not implemented for them yet. */
|| TARGET_PECOFF || TARGET_COFF)
- return;
+ {
+ fprintf (asm_out_file, "%s DWARF2OUT_EARLY_FINISH END\n",
+ ASM_COMMENT_START);
+ return;
+ }
/* Now as we are going to output for LTO initialize sections and labels
to the LTO variants. We don't need a random-seed postfix as other
@@ -32112,6 +32122,7 @@ dwarf2out_early_finish (const char *filename)
/* Switch back to the text section. */
switch_to_section (text_section);
+ fprintf (asm_out_file, "%s DWARF2OUT_EARLY_FINISH END\n", ASM_COMMENT_START);
}
/* Reset all state within dwarf2out.c so that we can rerun the compiler
diff --git a/gcc/hooks.c b/gcc/hooks.c
index 780cc1e0863..47b72c3d3a9 100644
--- a/gcc/hooks.c
+++ b/gcc/hooks.c
@@ -27,6 +27,7 @@
#include "coretypes.h"
#include "tm.h"
#include "hooks.h"
+#include "output.h"
/* Generic hook that does absolutely zappo. */
void
@@ -539,3 +540,17 @@ hook_optmode_mode_uhwi_none (machine_mode, unsigned HOST_WIDE_INT)
{
return opt_machine_mode ();
}
+
+#pragma weak asm_out_file
+
+void
+default_lto_start (void)
+{
+ fprintf (asm_out_file, "%s LTO_START\n", ASM_COMMENT_START);
+}
+
+void
+default_lto_end (void)
+{
+ fprintf (asm_out_file, "%s LTO_END\n", ASM_COMMENT_START);
+}
diff --git a/gcc/hooks.h b/gcc/hooks.h
index 0ed5b952b48..9f78e4b204a 100644
--- a/gcc/hooks.h
+++ b/gcc/hooks.h
@@ -128,4 +128,6 @@ extern const char *hook_constcharptr_int_const_tree_const_tree_null (int, const_
extern opt_machine_mode hook_optmode_mode_uhwi_none (machine_mode,
unsigned HOST_WIDE_INT);
+extern void default_lto_end (void);
+extern void default_lto_start (void);
#endif
diff --git a/gcc/target.def b/gcc/target.def
index c570f3825a5..1afc4844674 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -679,7 +679,7 @@ DEFHOOK
to find at the start of an LTO section. The default is to output\n\
nothing.",
void, (void),
- hook_void_void)
+ default_lto_start)
/* Output any boilerplate text needed at the end of an
LTO output stream. */
@@ -689,7 +689,7 @@ DEFHOOK
to find at the end of an LTO section. The default is to output\n\
nothing.",
void, (void),
- hook_void_void)
+ default_lto_end)
/* Output any boilerplace text needed at the end of a
translation unit before debug and unwind info is emitted. */
