20 Feb
2012
20 Feb
'12
8:52 p.m.
Hi All.
Recently at work I helped someone figure out that when working with ld,
the name of a function "foo" gets turned into "_foo" by the compiler.
(It took this old-timer 15 minutes to solve a problem he had been working
on for two days!)
I'm pretty sure this dates back to PDP-11 days. I'm wondering
"why?".
Why did the C compiler prepend an underscore to function names?
Thanks,
Arnold
20 Feb
20 Feb
11:21 p.m.
On Mon, 20 Feb 2012, arnold(a)skeeve.com wrote:
[...]
I'm pretty sure this dates back to PDP-11 days.
I'm wondering "why?".
Why did the C compiler prepend an underscore to function names?
Sure was the PDP-11 :-) I vaguely recall that it was to make sure that
user functions did not conflict with predefined assembler functions, as
that would be a pain to diagnose (much like having swap overlap root).
-- Dave
21 Feb
21 Feb
12:34 a.m.
correct. we could link to assembler code with _entry points and not worry about symbol
collisions in the rest of the code.
iPhone email
On Feb 20, 2012, at 6:23 PM, "Dave Horsfall" <dave(a)horsfall.org> wrote:
On Mon, 20 Feb 2012, arnold(a)skeeve.com wrote:
[...]
I'm pretty sure this dates back to PDP-11
days. I'm wondering "why?".
Why did the C compiler prepend an underscore to function names?
Sure was the PDP-11 :-) I vaguely recall that it was to make sure that
user functions did not conflict with predefined assembler functions, as
that would be a pain to diagnose (much like having swap overlap root).
-- Dave
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2:50 a.m.
And this convention went away with ELF binaries. No more _foo for function foo.
Also, the fortran compiler would emit entry_ to as to not conflict either. Made calling C
from Fortran, and vice versa, a lot of fun...
Warner
On Feb 20, 2012, at 5:34 PM, Brantley Coile wrote:
correct. we could link to assembler code with _entry
points and not worry about symbol collisions in the rest of the code.
iPhone email
On Feb 20, 2012, at 6:23 PM, "Dave Horsfall" <dave(a)horsfall.org> wrote:
On Mon, 20 Feb 2012, arnold(a)skeeve.com wrote:
[...]
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I'm pretty sure this dates back to PDP-11
days. I'm wondering "why?".
Why did the C compiler prepend an underscore to function names?
Sure was the PDP-11 :-) I vaguely recall that it was to make sure that
user functions did not conflict with predefined assembler functions, as
that would be a pain to diagnose (much like having swap overlap root).
-- Dave
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TUHS mailing list
TUHS(a)minnie.tuhs.org
https://minnie.tuhs.org/mailman/listinfo/tuhs 
3:33 a.m.
Warner Losh scripsit:
Also, the fortran compiler would emit entry_ to as to
not conflict
either. Made calling C from Fortran, and vice versa, a lot of fun...
Unix f77 emitted _foo_, that is, what C saw as foo_. In effect you
could call arbitrary Fortran routines from C, but not really vice versa:
in order to do so, the C functions had to have names ending in _ and use
the f77 type system.
--
A rabbi whose congregation doesn't want John Cowan
to drive him out of town isn't a rabbi, http://www.ccil.org/~cowan
and a rabbi who lets them do it cowan(a)ccil.org
isn't a man. --Jewish saying
3:41 a.m.
On Mon, 20 Feb 2012, Warner Losh wrote:
And this convention went away with ELF binaries. No
more _foo for
function foo.
Also, the fortran compiler would emit entry_ to as to not conflict
either. Made calling C from Fortran, and vice versa, a lot of fun...
Warner
Watcom C did the postfix style, dunno if it still does.
-uso.
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6 comments
7 participants
participants (7)
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arnold＠skeeve.com -
Brantley Coile -
Dave Horsfall -
John Cowan -
ron＠ronnatalie.com -
Steve Nickolas -
Warner Losh