This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: Rework the handling of assembler sections
Hans-Peter Nilsson <hp@bitrange.com> writes:
> On Wed, 7 Dec 2005, Richard Sandiford wrote:
>> The patch below fixes the testcases for arm-eabi. Could you check
>> whether it works for you?
>
> It works. Tested on mmix-knuth-mmixware, cris-axis-elf and
> cris-axis-linux-gnu. No regressions.
Thanks. Unfortunately, I don't think the patch is right. We would
no longer complain about .eh_frame conflicts if we happened to switch
to our internal section after finding a conflicting decl attribute.
(The patch even felt like a hack when I wrote last night, and in the
cold light of day...)
To recap, the changes I made in this area were:
> - The current exception_section and eh_frame_section hooks will
> switch to the same section every time they were called. I've
> therefore replaced them with global variables of the same name.
>
> eh_frame_section can be null if there's no dedicated section.
> This selects the code that used to be in collect2_eh_frame_section.
And the problem is that the old code would only create an eh_frame or
exception section when the hooks were first called, whereas the new code
creates them in init_varasm_once. This causes a new error if a TU did
not ever trigger calls to the old hooks and if that TU used the sections
with incompatible flags.
I hadn't anticipated that such code would exist. Given that it does
(and that it's in gcc itself) I now think the best fix is to back to
the lazy creation of eh_frame_section and exception_section.
The patch below does this. The aims were:
- To fix the bug, and reinstate the behaviour from before the
section patch.
- To keep the advantages of the current approach, such as the
once-per-compilation hashtable lookup.
- To continue to allow targets to override the sections in their
init_sections hook.
The two section variables are only used in one place each, as arguments
to switch_section. One of these uses is inside switch_to_eh_frame_section,
the other in output_function_exception_table. The patch replaces the latter
with a call to a new function, switch_to_exception_section, which serves
a similar purpose to the old exception_section target hook.
After the patch, switch_to_eh_frame_section will use the section cached
in eh_frame_section, if any, otherwise it will apply the usual default
rules. (The values cached in eh_frame_section will come either from the
target's init_sections hook or from earlier calls to the function.)
switch_to_exception_section behaves similarly for exception_section.
IMO, this is much cleaner than the patch I posted yesterday,
and diffstat likes it too. Bootstrapped & regression tested
on i686-pc-linux-gnu. OK to install?
Richard
* dwarf2out.c (default_eh_frame_section): Delete, moving handling
of EH_FRAME_SECTION_NAME into...
(switch_to_eh_frame_section): ...here. Try to set eh_frame_section
if it is still null.
* except.c (default_exception_section): Delete, moving most
of the code to...
(switch_to_exception_section): ...this new function. Set
exception_section if it is still null, then switch to it.
(output_function_exception_table): Use switch_to_exception_section.
* varasm.c (exception_section, eh_frame_section): Update comments.
(get_section): Hoist use of SECTION_NAMED.
(init_varasm_once): Don't set exception_section and eh_frame_section.
* output.h (default_exception_section): Delete.
(default_eh_frame_section): Delete.
testsuite/
* gcc.dg/20051207-1.c,
* gcc.dg/20051207-2.c,
* gcc.dg/20051207-3.c: New tests.
Index: gcc/testsuite/gcc.dg/20051207-2.c
===================================================================
--- gcc/testsuite/gcc.dg/20051207-2.c (revision 0)
+++ gcc/testsuite/gcc.dg/20051207-2.c (revision 0)
@@ -0,0 +1,5 @@
+/* GCC doesn't generate any .eh_frame data for this TU itself, so it
+ shouldn't warn about "a" conflicting with the built-in idea of
+ .eh_frame, even if it thinks that .eh_frame should be read-write. */
+/* { dg-require-named-sections "" } */
+const int a __attribute__((section (".eh_frame"))) = 1;
Index: gcc/testsuite/gcc.dg/20051207-1.c
===================================================================
--- gcc/testsuite/gcc.dg/20051207-1.c (revision 0)
+++ gcc/testsuite/gcc.dg/20051207-1.c (revision 0)
@@ -0,0 +1,5 @@
+/* GCC doesn't generate any .eh_frame data for this TU itself, so it
+ shouldn't warn about "a" conflicting with the built-in idea of
+ .eh_frame, even if it thinks that .eh_frame should be read-only. */
+/* { dg-require-named-sections "" } */
+int a __attribute__((section (".eh_frame"))) = 1;
Index: gcc/testsuite/gcc.dg/20051207-3.c
===================================================================
--- gcc/testsuite/gcc.dg/20051207-3.c (revision 0)
+++ gcc/testsuite/gcc.dg/20051207-3.c (revision 0)
@@ -0,0 +1,7 @@
+/* GCC doesn't generate any .eh_frame data for this TU itself, so it
+ shouldn't warn about "a" conflicting with the built-in idea of
+ .eh_frame. The warning therefore belongs on the second decl. */
+/* { dg-options "-fno-unit-at-a-time" } */
+/* { dg-require-named-sections "" } */
+int a __attribute__((section (".eh_frame"))) = 1;
+const int b __attribute__((section (".eh_frame"))) = 1; /* { dg-error "section type conflict" } */
Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c (revision 108162)
+++ gcc/dwarf2out.c (working copy)
@@ -113,42 +113,6 @@ dwarf2out_do_frame (void)
#define PTR_SIZE (POINTER_SIZE / BITS_PER_UNIT)
#endif
-/* Return the default value of eh_frame_section. Note that this function
- must appear outside the DWARF2_DEBUGGING_INFO || DWARF2_UNWIND_INFO
- macro guards. */
-
-section *
-default_eh_frame_section (void)
-{
-#ifdef EH_FRAME_SECTION_NAME
- int flags;
-
- if (EH_TABLES_CAN_BE_READ_ONLY)
- {
- int fde_encoding;
- int per_encoding;
- int lsda_encoding;
-
- fde_encoding = ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/1, /*global=*/0);
- per_encoding = ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/2, /*global=*/1);
- lsda_encoding = ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/0, /*global=*/0);
- flags = (! flag_pic
- || ((fde_encoding & 0x70) != DW_EH_PE_absptr
- && (fde_encoding & 0x70) != DW_EH_PE_aligned
- && (per_encoding & 0x70) != DW_EH_PE_absptr
- && (per_encoding & 0x70) != DW_EH_PE_aligned
- && (lsda_encoding & 0x70) != DW_EH_PE_absptr
- && (lsda_encoding & 0x70) != DW_EH_PE_aligned))
- ? 0 : SECTION_WRITE;
- }
- else
- flags = SECTION_WRITE;
- return get_section (EH_FRAME_SECTION_NAME, flags, NULL);
-#else
- return NULL;
-#endif
-}
-
DEF_VEC_P(rtx);
DEF_VEC_ALLOC_P(rtx,gc);
@@ -1993,10 +1957,44 @@ switch_to_eh_frame_section (void)
{
tree label;
+#ifdef EH_FRAME_SECTION_NAME
+ if (eh_frame_section == 0)
+ {
+ int flags;
+
+ if (EH_TABLES_CAN_BE_READ_ONLY)
+ {
+ int fde_encoding;
+ int per_encoding;
+ int lsda_encoding;
+
+ fde_encoding = ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/1,
+ /*global=*/0);
+ per_encoding = ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/2,
+ /*global=*/1);
+ lsda_encoding = ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/0,
+ /*global=*/0);
+ flags = ((! flag_pic
+ || ((fde_encoding & 0x70) != DW_EH_PE_absptr
+ && (fde_encoding & 0x70) != DW_EH_PE_aligned
+ && (per_encoding & 0x70) != DW_EH_PE_absptr
+ && (per_encoding & 0x70) != DW_EH_PE_aligned
+ && (lsda_encoding & 0x70) != DW_EH_PE_absptr
+ && (lsda_encoding & 0x70) != DW_EH_PE_aligned))
+ ? 0 : SECTION_WRITE);
+ }
+ else
+ flags = SECTION_WRITE;
+ eh_frame_section = get_section (EH_FRAME_SECTION_NAME, flags, NULL);
+ }
+#endif
+
if (eh_frame_section)
switch_to_section (eh_frame_section);
else
{
+ /* We have no special eh_frame section. Put the information in
+ the data section and emit special labels to guide collect2. */
switch_to_section (data_section);
label = get_file_function_name ('F');
ASM_OUTPUT_ALIGN (asm_out_file, floor_log2 (PTR_SIZE));
Index: gcc/except.c
===================================================================
--- gcc/except.c (revision 108162)
+++ gcc/except.c (working copy)
@@ -3425,30 +3425,34 @@ sjlj_output_call_site_table (void)
call_site_base += n;
}
-/* Return the default value of exception_section. */
+/* Switch to the section that should be used for exception tables. */
-section *
-default_exception_section (void)
+static void
+switch_to_exception_section (void)
{
- if (targetm.have_named_sections)
+ if (exception_section == 0)
{
- int flags;
-
- if (EH_TABLES_CAN_BE_READ_ONLY)
+ if (targetm.have_named_sections)
{
- int tt_format = ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/0, /*global=*/1);
-
- flags = (! flag_pic
- || ((tt_format & 0x70) != DW_EH_PE_absptr
- && (tt_format & 0x70) != DW_EH_PE_aligned))
- ? 0 : SECTION_WRITE;
+ int flags;
+
+ if (EH_TABLES_CAN_BE_READ_ONLY)
+ {
+ int tt_format =
+ ASM_PREFERRED_EH_DATA_FORMAT (/*code=*/0, /*global=*/1);
+ flags = ((! flag_pic
+ || ((tt_format & 0x70) != DW_EH_PE_absptr
+ && (tt_format & 0x70) != DW_EH_PE_aligned))
+ ? 0 : SECTION_WRITE);
+ }
+ else
+ flags = SECTION_WRITE;
+ exception_section = get_section (".gcc_except_table", flags, NULL);
}
else
- flags = SECTION_WRITE;
- return get_section (".gcc_except_table", flags, NULL);
+ exception_section = flag_pic ? data_section : readonly_data_section;
}
- else
- return flag_pic ? data_section : readonly_data_section;
+ switch_to_section (exception_section);
}
@@ -3530,7 +3534,7 @@ output_function_exception_table (void)
/* Note that varasm still thinks we're in the function's code section.
The ".endp" directive that will immediately follow will take us back. */
#else
- switch_to_section (exception_section);
+ switch_to_exception_section ();
#endif
have_tt_data = (VEC_length (tree, cfun->eh->ttype_data) > 0
Index: gcc/varasm.c
===================================================================
--- gcc/varasm.c (revision 108162)
+++ gcc/varasm.c (working copy)
@@ -155,12 +155,14 @@ static void mark_weak (tree);
section *init_section;
section *fini_section;
-/* The section that holds the main exception table. */
+/* The section that holds the main exception table, when known. The section
+ is set either by the target's init_sections hook or by the first call to
+ switch_to_exception_section. */
section *exception_section;
-/* The section that holds the DWARF2 frame unwind information. If it
- is null, we will place the unwind information in the data section
- and emit special labels to guide collect2. */
+/* The section that holds the DWARF2 frame unwind information, when known.
+ The section is set either by the target's init_sections hook or by the
+ first call to switch_to_eh_frame_section. */
section *eh_frame_section;
/* asm_out_file's current section. This is NULL if no section has yet
@@ -230,10 +232,11 @@ get_section (const char *name, unsigned
slot = (section **)
htab_find_slot_with_hash (section_htab, name,
htab_hash_string (name), INSERT);
+ flags |= SECTION_NAMED;
if (*slot == NULL)
{
sect = ggc_alloc (sizeof (struct named_section));
- sect->named.common.flags = flags | SECTION_NAMED;
+ sect->named.common.flags = flags;
sect->named.name = ggc_strdup (name);
sect->named.decl = decl;
*slot = sect;
@@ -241,7 +244,7 @@ get_section (const char *name, unsigned
else
{
sect = *slot;
- if ((sect->common.flags & ~(SECTION_DECLARED | SECTION_NAMED)) != flags
+ if ((sect->common.flags & ~SECTION_DECLARED) != flags
&& ((sect->common.flags | flags) & SECTION_OVERRIDE) == 0)
{
/* Sanity check user variables for flag changes. */
@@ -4868,10 +4871,6 @@ init_varasm_once (void)
if (readonly_data_section == NULL)
readonly_data_section = text_section;
- if (exception_section == NULL)
- exception_section = default_exception_section ();
- if (eh_frame_section == NULL)
- eh_frame_section = default_eh_frame_section ();
}
enum tls_model
Index: gcc/output.h
===================================================================
--- gcc/output.h (revision 108162)
+++ gcc/output.h (working copy)
@@ -384,12 +384,6 @@ extern int compute_reloc_for_constant (t
/* Default target function prologue and epilogue assembler output. */
extern void default_function_pro_epilogue (FILE *, HOST_WIDE_INT);
-/* Return the default value of exception_section. */
-extern section *default_exception_section (void);
-
-/* Return the default value of eh_frame_section. */
-extern section *default_eh_frame_section (void);
-
/* Default target hook that outputs nothing to a stream. */
extern void no_asm_to_stream (FILE *);