linux-kernel - [PATCH] scripts/kallsyms: Fix build failure by setting errno before calling getline()

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Date:   Mon, 24 Jul 2023 14:17:40 +0100
From:   James Clark <james.clark@....com>
To:     linux-kbuild@...r.kernel.org, masahiroy@...nel.org
Cc:     linux-kernel@...r.kernel.org, James Clark <james.clark@....com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Nicolas Schier <n.schier@....de>
Subject: [PATCH] scripts/kallsyms: Fix build failure by setting errno before calling getline()

getline() returns -1 at EOF as well as on error. It also doesn't set
errno to 0 on success, so initialize it to 0 before using errno to check
for an error condition. See the paragraph here [1]:

  For some system calls and library functions (e.g., getpriority(2)),
  -1 is a valid return on success. In such cases, a successful return
  can be distinguished from an error return by setting errno to zero
  before the call, and then, if the call returns a status that indicates
  that an error may have occurred, checking to see if errno has a
  nonzero value.

This fixes the following build failure if scripts/kallsyms launches with
a non-zero errno value:

 $ make
 ...
  LD      .tmp_vmlinux.kallsyms1
  NM      .tmp_vmlinux.kallsyms1.syms
  KSYMS   .tmp_vmlinux.kallsyms1.S
 read_symbol: Invalid argument

[1]: https://linux.die.net/man/3/errno

Fixes: 1c975da56a6f ("scripts/kallsyms: remove KSYM_NAME_LEN_BUFFER")
Signed-off-by: James Clark <james.clark@....com>
---
 scripts/kallsyms.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 16c87938b316..653b92f6d4c8 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -129,6 +129,7 @@ static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
 	ssize_t readlen;
 	struct sym_entry *sym;
 
+	errno = 0;
 	readlen = getline(buf, buf_len, in);
 	if (readlen < 0) {
 		if (errno) {
-- 
2.34.1