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mainUtils: match readline behavior when ABC_USE_READLINE is undefined 

The non-readline branch of Abc_UtilsGetUsersInput has three behavioral
gaps versus the readline branch that break callers driving abc as a
coprocess over a pipe (e.g. yosys's passes/techmap/abc.cc, which spawns
"abc -s" with piped stdin/stdout and uses read_until_abc_done to wait
for "abc NN> <command>" lines):

  1. The prompt is written with fprintf() and never flushed. On a pipe
     stdout is fully buffered, so the prompt never reaches the reader.
     The reader waits for the prompt, abc waits in fgets(), deadlock.

  2. There is no echo of the line read from stdin. readline() emits
     each character to its output stream; yosys's protocol depends on
     seeing "abc NN> source ...\n" in the output to advance state.
     Without an echo it waits forever.

  3. EOF on stdin is silently ignored: fgets() returns NULL but the
     function returns a stale Prompt buffer, causing a tight loop on
     pipe close. The readline branch exit(0)s on NULL.

Fix all three. Echo only when stdin is not a tty -- on a tty the kernel
already echoes typed characters during cooked input, so double-echo
would be visible to interactive users.

Signed-off-by: Matt Liberty <mliberty@precisioninno.com>
This commit is contained in:
Matt Liberty 2026-06-05 06:05:32 +00:00
parent 21b2d8959a
commit 66f5d7c7a2
1 changed files with 8 additions and 0 deletions
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8
src/base/main/mainUtils.c
View File

@ -18,6 +18,8 @@
***********************************************************************/
#include <unistd.h>
#include "base/abc/abc.h"
#include "mainInt.h"
@ -91,7 +93,13 @@ char * Abc_UtilsGetUsersInput( Abc_Frame_t * pAbc )
{
char * pRetValue;
fprintf( pAbc->Out, "%s", Prompt );
fflush( pAbc->Out );
pRetValue = fgets( Prompt, 5000, stdin );
if ( pRetValue == NULL ) { exit(0); }
if ( !isatty( fileno(stdin) ) ) {
fputs( Prompt, pAbc->Out );
fflush( pAbc->Out );
}
return Prompt;
}
#endif