bug#31708: 'gcc-strmov-store-file-names.patch' causes GCC segfaults

[ludo@gnu.org (Ludovic Courtès)]

Hello,

On current ‘core-updates’, we have:

--8<---------------cut here---------------start------------->8---
$ readlink -f $(type -P gcc)
/gnu/store/zrhwhlqqk51qslbddk4cip2z2p3fpvxd-gcc-5.5.0/bin/gcc
ludo@ribbon /home/ludo/src/guix/+core-updates$ cat strmov-ice.c
#define _GNU_SOURCE
#include <string.h>

void foo (char *x)
{
  static const char buf[12];
  memcpy (x, buf, 12);
}
$ gcc -dH -O2 -Wall -c strmov-ice.c
strmov-ice.c: In function ‘foo’:
strmov-ice.c:7:3: internal compiler error: Segmentation fault
   memcpy (x, buf, 12);
   ^
gcc: internal compiler error: Aborted (program cc1)
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
$ gdb /gnu/store/zrhwhlqqk51qslbddk4cip2z2p3fpvxd-gcc-5.5.0/libexec/gcc/x86_64-unknown-linux-gnu/5.5.0/cc1 core 
GNU gdb (GDB) 8.1
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and "show warranty" for details.
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Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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For help, type "help".
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Reading symbols from /gnu/store/zrhwhlqqk51qslbddk4cip2z2p3fpvxd-gcc-5.5.0/libexec/gcc/x86_64-unknown-linux-gnu/5.5.0/cc1...(no debugging symbols found)...done.
[New LWP 1694]
Core was generated by `/gnu/store/zrhwhlqqk51qslbddk4cip2z2p3fpvxd-gcc-5.5.0/libexec/gcc/x86_64-unknow'.
Program terminated with signal SIGABRT, Aborted.
#0  0x00007fc415d8ba50 in raise () from /gnu/store/l4lr0f5cjd0nbsaaf8b5dmcw1a1yypr3-glibc-2.27/lib/libc.so.6
(gdb) bt
#0  0x00007fc415d8ba50 in raise () from /gnu/store/l4lr0f5cjd0nbsaaf8b5dmcw1a1yypr3-glibc-2.27/lib/libc.so.6
#1  0x00007fc415d8cc31 in abort () from /gnu/store/l4lr0f5cjd0nbsaaf8b5dmcw1a1yypr3-glibc-2.27/lib/libc.so.6
#2  0x0000000000f947ab in diagnostic_action_after_output(diagnostic_context*, diagnostic_t) ()
#3  0x0000000000f94a60 in diagnostic_report_diagnostic(diagnostic_context*, diagnostic_info*) ()
#4  0x0000000000f95a88 in internal_error(char const*, ...) ()
#5  0x00000000009e9b40 in crash_signal(int) ()
#6  <signal handler called>
#7  0x00000000006b3404 in store_reference_p(tree_node*) ()
#8  0x00000000007f4880 in gimple_fold_builtin_memory_op(gimple_stmt_iterator*, tree_node*, tree_node*, int) ()
#9  0x00000000007f643e in gimple_fold_builtin(gimple_stmt_iterator*) ()
#10 0x00000000007f8cf4 in fold_stmt_1(gimple_stmt_iterator*, bool, tree_node* (*)(tree_node*)) ()
#11 0x0000000000843c68 in gimplify_call_expr(tree_node**, gimple_statement_base**, bool) ()
#12 0x000000000083f5c8 in gimplify_expr(tree_node**, gimple_statement_base**, gimple_statement_base**, bool (*)(tree_node*), int) ()
#13 0x0000000000840ad7 in gimplify_stmt(tree_node**, gimple_statement_base**) ()
#14 0x000000000083effc in gimplify_expr(tree_node**, gimple_statement_base**, gimple_statement_base**, bool (*)(tree_node*), int) ()
#15 0x0000000000840ad7 in gimplify_stmt(tree_node**, gimple_statement_base**) ()
#16 0x00000000008412de in gimplify_bind_expr(tree_node**, gimple_statement_base**) ()
#17 0x000000000083f5aa in gimplify_expr(tree_node**, gimple_statement_base**, gimple_statement_base**, bool (*)(tree_node*), int) ()
#18 0x0000000000840ad7 in gimplify_stmt(tree_node**, gimple_statement_base**) ()
#19 0x0000000000841982 in gimplify_body(tree_node*, bool) ()
#20 0x0000000000841ca8 in gimplify_function_tree(tree_node*) ()
#21 0x00000000006fa268 in cgraph_node::analyze() ()
#22 0x00000000006fc870 in analyze_functions() ()
#23 0x00000000006fccb8 in symbol_table::finalize_compilation_unit() ()
#24 0x0000000000611183 in c_write_global_declarations() ()
#25 0x00000000009e9bd3 in compile_file() ()
#26 0x00000000005f0214 in toplev::main(int, char**) ()
#27 0x00000000005f0f7e in main ()
--8<---------------cut here---------------end--------------->8---

This is because DECL_INITIAL returns NULL_TREE for ‘buf’, but
‘store_reference_p’ doesn’t check whether we got NULL_TREE.

The fix is very simple (adding a NULL_TREE check), but in the meantime
we need to work around it.

A simple workaround is to pass an initializer to the static const array:

--8<---------------cut here---------------start------------->8---
$ cat strmov-ice.c
#define _GNU_SOURCE
#include <string.h>

void foo (char *x)
{
  static const char buf[12] = { 0, };
  memcpy (x, buf, 12);
}
$ gcc -dH -O2 -Wall -c strmov-ice.c
$ echo $?
0
--8<---------------cut here---------------end--------------->8---

The meaning of the program is unchanged but the bug is not triggered.

“Apologies for the inconvenience and thank you for your understanding”
as they say.

Ludo’.