From: Fangrui Song <i@maskray.me>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: binutils@sourceware.org
Subject: Re: [PATCH] ELF: Discard a section if any of its linked-to section has been discarded
Date: Sat, 08 Feb 2020 18:14:00 -0000 [thread overview]
Message-ID: <20200208181425.eob7jcssy2gery6o@google.com> (raw)
In-Reply-To: <20200207021431.387289-1-hjl.tools@gmail.com>
On 2020-02-06, H.J. Lu wrote:
>Add ldelf_before_place_orphans to call before lang_place_orphans to
>discard a section if any of its linked-to sections has been discarded.
>
> PR ld/25022
> * emultempl/aix.em (ld_${EMULATION_NAME}_emulation): Add
> before_place_orphans_default.
> * emultempl/armcoff.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/beos.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/generic.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/linux.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/msp430.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/pe.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/pep.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/ticoff.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/vanilla.em (ld_${EMULATION_NAME}_emulation): Likewise.
> * emultempl/elf.em (ld_${EMULATION_NAME}_emulation): Use
> ldelf_before_place_orphans.
> * ldelf.c (ldelf_before_place_orphans): New.
> * ldelf.h (ldelf_before_place_orphans): Likewise.
> * ldemul.c (ldemul_before_place_orphans): Likewise.
> (before_place_orphans_default): Likewise.
> * ldemul.h (ldemul_before_place_orphans): Likewise.
> (before_place_orphans_default): Likewise.
> (ld_emulation_xfer_struct): Add before_place_orphans.
> * ldlang.c (lang_process): Call ldemul_before_place_orphans
> before lang_place_orphans.
> * testsuite/ld-elf/pr25022.d: New file.
> * testsuite/ld-elf/pr25022.s: Likewise.
> * testsuite/ld-elf/pr25022.t: Likewise.
>---
> ld/emultempl/aix.em | 1 +
> ld/emultempl/armcoff.em | 1 +
> ld/emultempl/beos.em | 1 +
> ld/emultempl/elf.em | 1 +
> ld/emultempl/generic.em | 1 +
> ld/emultempl/linux.em | 1 +
> ld/emultempl/msp430.em | 1 +
> ld/emultempl/pe.em | 1 +
> ld/emultempl/pep.em | 1 +
> ld/emultempl/ticoff.em | 1 +
> ld/emultempl/vanilla.em | 1 +
> ld/ldelf.c | 29 +++++++++++++++++++++++++++++
> ld/ldelf.h | 1 +
> ld/ldemul.c | 11 +++++++++++
> ld/ldemul.h | 7 +++++++
> ld/ldlang.c | 2 ++
> ld/testsuite/ld-elf/pr25022.d | 9 +++++++++
> ld/testsuite/ld-elf/pr25022.s | 11 +++++++++++
> ld/testsuite/ld-elf/pr25022.t | 1 +
> 19 files changed, 82 insertions(+)
> create mode 100644 ld/testsuite/ld-elf/pr25022.d
> create mode 100644 ld/testsuite/ld-elf/pr25022.s
> create mode 100644 ld/testsuite/ld-elf/pr25022.t
>
>diff --git a/ld/emultempl/aix.em b/ld/emultempl/aix.em
>index c39491eab43..2da38709899 100644
>--- a/ld/emultempl/aix.em
>+++ b/ld/emultempl/aix.em
>@@ -1541,6 +1541,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation = {
> after_parse_default,
> gld${EMULATION_NAME}_after_open,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> gld${EMULATION_NAME}_set_output_arch,
> gld${EMULATION_NAME}_choose_target,
>diff --git a/ld/emultempl/armcoff.em b/ld/emultempl/armcoff.em
>index 0528c637b68..c539e2facca 100644
>--- a/ld/emultempl/armcoff.em
>+++ b/ld/emultempl/armcoff.em
>@@ -263,6 +263,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> after_parse_default,
> gld${EMULATION_NAME}_after_open,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> set_output_arch_default,
> ldemul_default_target,
>diff --git a/ld/emultempl/beos.em b/ld/emultempl/beos.em
>index 97cde99c335..2c3e5e5370d 100644
>--- a/ld/emultempl/beos.em
>+++ b/ld/emultempl/beos.em
>@@ -763,6 +763,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> after_parse_default,
> gld_${EMULATION_NAME}_after_open,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> set_output_arch_default,
> ldemul_default_target,
>diff --git a/ld/emultempl/elf.em b/ld/emultempl/elf.em
>index 42c552b36ed..bb7e5375303 100644
>--- a/ld/emultempl/elf.em
>+++ b/ld/emultempl/elf.em
>@@ -880,6 +880,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> ${LDEMUL_AFTER_PARSE-ldelf_after_parse},
> ${LDEMUL_AFTER_OPEN-gld${EMULATION_NAME}_after_open},
> ${LDEMUL_AFTER_CHECK_RELOCS-after_check_relocs_default},
>+ ${LDEMUL_BEFORE_PLACE_ORPHANS-ldelf_before_place_orphans},
> ${LDEMUL_AFTER_ALLOCATION-gld${EMULATION_NAME}_after_allocation},
> ${LDEMUL_SET_OUTPUT_ARCH-set_output_arch_default},
> ${LDEMUL_CHOOSE_TARGET-ldemul_default_target},
>diff --git a/ld/emultempl/generic.em b/ld/emultempl/generic.em
>index e140514e8ef..a39c9332075 100644
>--- a/ld/emultempl/generic.em
>+++ b/ld/emultempl/generic.em
>@@ -138,6 +138,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> ${LDEMUL_AFTER_PARSE-after_parse_default},
> ${LDEMUL_AFTER_OPEN-after_open_default},
> ${LDEMUL_AFTER_CHECK_RELOCS-after_check_relocs_default},
>+ ${LDEMUL_BEFORE_PLACE_ORPHANS-before_place_orphans_default},
> ${LDEMUL_AFTER_ALLOCATION-after_allocation_default},
> ${LDEMUL_SET_OUTPUT_ARCH-set_output_arch_default},
> ${LDEMUL_CHOOSE_TARGET-ldemul_default_target},
>diff --git a/ld/emultempl/linux.em b/ld/emultempl/linux.em
>index fea8da486dc..f4ae6cfba29 100644
>--- a/ld/emultempl/linux.em
>+++ b/ld/emultempl/linux.em
>@@ -190,6 +190,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> after_parse_default,
> after_open_default,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> set_output_arch_default,
> ldemul_default_target,
>diff --git a/ld/emultempl/msp430.em b/ld/emultempl/msp430.em
>index df940672bac..861c1dcda0a 100644
>--- a/ld/emultempl/msp430.em
>+++ b/ld/emultempl/msp430.em
>@@ -825,6 +825,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> ${LDEMUL_AFTER_PARSE-after_parse_default},
> msp430_elf_after_open,
> after_check_relocs_default,
>+ before_place_orphans_default,
> msp430_elf_after_allocation,
> ${LDEMUL_SET_OUTPUT_ARCH-set_output_arch_default},
> ${LDEMUL_CHOOSE_TARGET-ldemul_default_target},
>diff --git a/ld/emultempl/pe.em b/ld/emultempl/pe.em
>index 97fb1468aac..db23b221d66 100644
>--- a/ld/emultempl/pe.em
>+++ b/ld/emultempl/pe.em
>@@ -2354,6 +2354,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> gld_${EMULATION_NAME}_after_parse,
> gld_${EMULATION_NAME}_after_open,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> set_output_arch_default,
> ldemul_default_target,
>diff --git a/ld/emultempl/pep.em b/ld/emultempl/pep.em
>index e8f5ca503fb..3d09a0a6b13 100644
>--- a/ld/emultempl/pep.em
>+++ b/ld/emultempl/pep.em
>@@ -2153,6 +2153,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> gld_${EMULATION_NAME}_after_parse,
> gld_${EMULATION_NAME}_after_open,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> set_output_arch_default,
> ldemul_default_target,
>diff --git a/ld/emultempl/ticoff.em b/ld/emultempl/ticoff.em
>index 2b6fae64a08..60c0da9f1b1 100644
>--- a/ld/emultempl/ticoff.em
>+++ b/ld/emultempl/ticoff.em
>@@ -163,6 +163,7 @@ struct ld_emulation_xfer_struct ld_${EMULATION_NAME}_emulation =
> after_parse_default,
> after_open_default,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> set_output_arch_default,
> ldemul_default_target,
>diff --git a/ld/emultempl/vanilla.em b/ld/emultempl/vanilla.em
>index e17316fb5a2..ae6f6e4175d 100644
>--- a/ld/emultempl/vanilla.em
>+++ b/ld/emultempl/vanilla.em
>@@ -64,6 +64,7 @@ struct ld_emulation_xfer_struct ld_vanilla_emulation =
> after_parse_default,
> after_open_default,
> after_check_relocs_default,
>+ before_place_orphans_default,
> after_allocation_default,
> vanilla_set_output_arch,
> ldemul_default_target,
>diff --git a/ld/ldelf.c b/ld/ldelf.c
>index 2e27cf48a81..3ac3bb4e0a5 100644
>--- a/ld/ldelf.c
>+++ b/ld/ldelf.c
>@@ -2134,3 +2134,32 @@ ldelf_place_orphan (asection *s, const char *secname, int constraint)
>
> return lang_insert_orphan (s, secname, constraint, after, place, NULL, NULL);
> }
>+
>+void
>+ldelf_before_place_orphans (void)
>+{
>+ bfd *abfd;
>+
>+ for (abfd = link_info.input_bfds;
>+ abfd != (bfd *) NULL; abfd = abfd->link.next)
>+ if (bfd_get_flavour (abfd) == bfd_target_elf_flavour
>+ && bfd_count_sections (abfd) != 0
>+ && !bfd_input_just_syms (abfd))
>+ {
>+ asection *isec;
>+ for (isec = abfd->sections; isec != NULL; isec = isec->next)
>+ {
>+ /* Discard a section if any of its linked-to section has
>+ been discarded. */
>+ asection *linked_to_sec;
>+ for (linked_to_sec = elf_linked_to_section (isec);
>+ linked_to_sec != NULL;
>+ linked_to_sec = elf_linked_to_section (linked_to_sec))
>+ if (discarded_section (linked_to_sec))
>+ {
>+ isec->output_section = bfd_abs_section_ptr;
>+ break;
>+ }
>+ }
>+ }
>+}
>diff --git a/ld/ldelf.h b/ld/ldelf.h
>index 492649b2934..2a58a0c1359 100644
>--- a/ld/ldelf.h
>+++ b/ld/ldelf.h
>@@ -30,3 +30,4 @@ extern bfd_boolean ldelf_open_dynamic_archive
> (const char *, search_dirs_type *, lang_input_statement_type *);
> extern lang_output_section_statement_type *ldelf_place_orphan
> (asection *, const char *, int);
>+extern void ldelf_before_place_orphans (void);
>diff --git a/ld/ldemul.c b/ld/ldemul.c
>index 1f5228d2a4a..fa6dfdd18ed 100644
>--- a/ld/ldemul.c
>+++ b/ld/ldemul.c
>@@ -71,6 +71,12 @@ ldemul_after_check_relocs (void)
> ld_emulation->after_check_relocs ();
> }
>
>+void
>+ldemul_before_place_orphans (void)
>+{
>+ ld_emulation->before_place_orphans ();
>+}
>+
> void
> ldemul_after_allocation (void)
> {
>@@ -266,6 +272,11 @@ after_check_relocs_default (void)
> {
> }
>
>+void
>+before_place_orphans_default (void)
>+{
>+}
>+
> void
> after_allocation_default (void)
> {
>diff --git a/ld/ldemul.h b/ld/ldemul.h
>index bde74dfa9a1..44e3a92aa7e 100644
>--- a/ld/ldemul.h
>+++ b/ld/ldemul.h
>@@ -36,6 +36,8 @@ extern void ldemul_after_open
> (void);
> extern void ldemul_after_check_relocs
> (void);
>+extern void ldemul_before_place_orphans
>+ (void);
> extern void ldemul_after_allocation
> (void);
> extern void ldemul_before_allocation
>@@ -80,6 +82,8 @@ extern void after_open_default
> (void);
> extern void after_check_relocs_default
> (void);
>+extern void before_place_orphans_default
>+ (void);
> extern void after_allocation_default
> (void);
> extern void before_allocation_default
>@@ -129,6 +133,9 @@ typedef struct ld_emulation_xfer_struct {
> /* Run after checking relocations. */
> void (*after_check_relocs) (void);
>
>+ /* Run before placing orphans. */
>+ void (*before_place_orphans) (void);
>+
> /* Run after allocating output sections. */
> void (*after_allocation) (void);
>
>diff --git a/ld/ldlang.c b/ld/ldlang.c
>index 91c160b5604..528ed22c1bc 100644
>--- a/ld/ldlang.c
>+++ b/ld/ldlang.c
>@@ -7837,6 +7837,8 @@ lang_process (void)
> output statement, so that it isn't reordered. */
> process_insert_statements (&lang_os_list.head->header.next);
>
>+ ldemul_before_place_orphans ();
>+
> /* Find any sections not attached explicitly and handle them. */
> lang_place_orphans ();
>
>diff --git a/ld/testsuite/ld-elf/pr25022.d b/ld/testsuite/ld-elf/pr25022.d
>new file mode 100644
>index 00000000000..9a397523a31
>--- /dev/null
>+++ b/ld/testsuite/ld-elf/pr25022.d
>@@ -0,0 +1,9 @@
>+#ld: -T pr25022.t
>+#readelf: -SW
>+#xfail: msp*-*
>+# msp* doesn't use ldelf_before_place_orphans.
>+
>+#failif
>+#...
>+ +\[ *[0-9]+\] \.(bar|moo|zed) +.*
>+#...
>diff --git a/ld/testsuite/ld-elf/pr25022.s b/ld/testsuite/ld-elf/pr25022.s
>new file mode 100644
>index 00000000000..ace4f25f2bc
>--- /dev/null
>+++ b/ld/testsuite/ld-elf/pr25022.s
>@@ -0,0 +1,11 @@
>+ .section .foo,"a"
>+ .dc.a 0
>+
>+ .section .moo,"ao",%progbits,.zed
>+ .dc.a 0
>+
>+ .section .bar,"ao",%progbits,.foo
>+ .dc.a 0
>+
>+ .section .zed,"ao",%progbits,.foo
>+ .dc.a 0
>diff --git a/ld/testsuite/ld-elf/pr25022.t b/ld/testsuite/ld-elf/pr25022.t
>new file mode 100644
>index 00000000000..bb9aa81e0f3
>--- /dev/null
>+++ b/ld/testsuite/ld-elf/pr25022.t
>@@ -0,0 +1 @@
>+SECTIONS { /DISCARD/ : { *(.foo) } }
>--
>2.24.1
Is the second rule listed on
https://sourceware.org/ml/binutils/2020-02/msg00035.html respected?
> For a non-SHF_ALLOC section, it is a GC root only if all the following
> conditions are satisfied:
> ...
> * it is not in a section group with at least one SHF_ALLOC section.
> If it belongs to such a section group, we expect a
> SHF_ALLOC section in the section group responsible for making the
> whole group alive. This semantic is at least expected by
If A (with SHF_LINK_ORDER) is in a section group with no SHF_ALLOC
section, we should not garbage collect A.
next prev parent reply other threads:[~2020-02-08 18:14 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-07 2:14 H.J. Lu
2020-02-07 3:30 ` Alan Modra
2020-02-08 18:14 ` Fangrui Song [this message]
2020-02-08 20:23 ` H.J. Lu
-- strict thread matches above, loose matches on Subject: below --
2020-02-03 14:39 H.J. Lu
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