https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116483
Bug ID: 116483
Summary: RFE: a notion for asm goto to indicate all labels in
the function may be jumped to
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: xry111 at gcc dot gnu.org
Target Milestone: ---
Hi,
We currently have some code using computed goto:
goto *table[index];
But for satisfying some tools analyzing the generated machine code, we need to
encode the address of the jump instruction and the address of the table in a
special section, something like.
asm volatile (
"1:"
"jr %0\n\t"
".pushsection .metainfo\n\t"
" .8byte 1b\n\t"
" .8byte %1\n\t"
".popsection"
: "r"(table[index]), "r"(table)
);
But this won't work: the compiler does not know this asm block ever jumps. To
make it aware of the jump, we have to do:
asm goto (
"1:"
"jr %0\n\t"
".pushsection .metainfo\n\t"
" .8byte 1b\n\t"
" .8byte %1\n\t"
".popsection"
: "r"(table[index]), "r"(table)
:
:
: label1, label2, label3, label4, label5 /* ... */
);
Unfortunately this is nasty with a hundred of labels. So IMO it may be useful
to add a notion to indicate this asm goto block may jump into any label in the
same function, maybe like...
asm goto (
"1:"
"jr %0\n\t"
".pushsection .metainfo\n\t"
" .8byte 1b\n\t"
" .8byte %1\n\t"
".popsection"
: "r"(table[index]), "r"(table)
:
:
: "anywhere"
);
?
