[PATCH 11/31] pahole: Fix --errno typo that decrements instead of negating

From: Arnaldo Carvalho de Melo <[email protected]>

prototype__stdio_fprintf_value() uses --errno in three error paths,
which decrements the global errno value instead of negating it with
-errno.  This causes the function to return a wrong (often positive)
value on error, making callers think the operation succeeded.

Before: --errno with errno=5 returns 4 (positive, looks like success)
After:  -errno with errno=5 returns -5 (negative, correctly signals error)

Fixes: 9310b04854a8b709 ("pahole: Add support for referencing header variables when pretty printing")
Reported-by: Sashiko:gemini-3-1-pro-preview
Assisted-by: Claude:claude-sonnet-4-5
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
---
 pahole.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pahole.c b/pahole.c
index 0096dfa34e5047c8..6ba3f578c28570a1 100644
--- a/pahole.c
+++ b/pahole.c
@@ -2584,7 +2584,7 @@ static int prototype__stdio_fprintf_value(struct prototype *prototype, struct ty
 		return -ENOMEM;
 
 	if (type__instance_read_once(header, input) < 0) {
-		printed = --errno;
+		printed = -errno;
 		fprintf(stderr, "pahole: --header (%s) type couldn't be read\n", conf.header_type);
 		goto out;
 	}
@@ -2667,7 +2667,7 @@ static int prototype__stdio_fprintf_value(struct prototype *prototype, struct ty
 		free(member_name);
 
 		if (pipe_seek(input, seek_bytes) < 0) {
-			printed = --errno;
+			printed = -errno;
 			fprintf(stderr, "Couldn't --seek_bytes %s (%" PRIu64 "\n", conf.seek_bytes, seek_bytes);
 			goto out;
 		}
@@ -2718,7 +2718,7 @@ static int prototype__stdio_fprintf_value(struct prototype *prototype, struct ty
 		}
 
 		if (pipe_seek(input, seek_bytes) < 0) {
-			printed = --errno;
+			printed = -errno;
 			fprintf(stderr, "Couldn't --seek_bytes %s (%" PRIu64 "\n", conf.seek_bytes, seek_bytes);
 			goto out;
 		}
-- 
2.55.0