https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88641
Bug ID: 88641
Summary: crtstuff.c ctors/dtors list breaks with
-fdata-sections
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgcc
Assignee: unassigned at gcc dot gnu.org
Reporter: ambrop7 at gmail dot com
Target Milestone: ---
Created attachment 45309
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45309&action=edit
Patch to compile crtstuff.c with -fno-function-sections and -fno-data-sections.
Breakage of ctors/dtors lists in crtbegin.o/crtend.o may occur when
CFLAGS_FOR_TARGET contains -fdata-sections, leading to a crash at program
startup.
The issue is in libgcc/crtstuff.c where __LIBGCC_CTORS_SECTION_ASM_OP__ is
used. I have experienced this with the MicroBlaze architecture, but any
architecture where this code path is used has to be affected. Specifically, the
problem is in the following code:
static func_ptr force_to_data[1] __attribute__ ((__used__)) = { };
asm (__LIBGCC_CTORS_SECTION_ASM_OP__);
STATIC func_ptr __CTOR_LIST__[1]
__attribute__ ((__used__, aligned(sizeof(func_ptr))))
= { (func_ptr) (-1) };
Here asm is used to make the variable go into a specific section, usually
".ctors" or ".dtors". However, with -fdata-sections, gcc will anyway put it
into its own section such as ".data.__CTOR_LIST__", and the asm will have no
effect. The result is that these variables will not be found by the linker
script using expressions like "KEEP (*crtbegin.o(.ctors))", which will cause a
runtime failure in __do_global_ctors_aux as the ctors list will have no
terminator.
I believe that -ffunction-section could also cause problems in the crtstuff
code, in particular where __LIBGCC_TEXT_SECTION_ASM_OP__ is used; there seems
to be an assumption that all functions are by default placed in the ".text"
section, which is not true with -ffunction-sections.
I suggest fixing these issues by ensuring that crtstuff.c is compiled with
-fno-function-sections and -fno-data-sections. I am attaching a patch that I
have verified fixes the ctors/dtors section problem.
