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From 40c112ed0d7d0577d2f84851c1f7b8157b3bd2f5 Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Mon, 31 Oct 2022 15:46:38 -0300
Subject: [PATCH] elf: Remove allocate use on _dl_debug_printf
The maximum number of directives is already limited by the maximum
value of iovec, and current padding usage on _dl_map_object_from_fd
specifies a value of 16 (2 times sizeof (void *)) in hexa, which is
less than the INT_STRLEN_BOUND(void *) (20 for LP64).
This works if pointers are larger than 8 bytes, for instance 16.
In this case the maximum padding would be 32 and the IFMTSIZE would
be 40.
The resulting code does use a slightly larger static stack, the
output of -fstack-usage (for x86_64):
* master:
dl-printf.c:35:1:_dl_debug_vdprintf 1344 dynamic
* patch:
dl-printf.c:36:1:_dl_debug_vdprintf 2416 static
However, there is an improvement in code generation:
* master
text data bss dec hex filename
330900 3309 ced elf/dl-printf.os
* patch
text data bss dec hex filename
315100 3151 c4f elf/dl-printf.os
Checked on x86_64-linux-gnu.
Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
---
elf/dl-misc.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/elf/dl-misc.c b/elf/dl-misc.c
index a11d11d5..4a33737c 100644
--- a/elf/dl-misc.c
+++ b/elf/dl-misc.c
@@ -34,6 +34,7 @@
#include <_itoa.h>
#include <dl-writev.h>
#include <not-cancel.h>
+#include <intprops.h>
/* Read the whole contents of FILE into new mmap'd space with given
protections. *SIZEP gets the size of the file. On error MAP_FAILED
@@ -79,6 +80,9 @@ _dl_debug_vdprintf (int fd, int tag_p, const char *fmt, va_list arg)
{
# define NIOVMAX 64
struct iovec iov[NIOVMAX];
+ /* Maximum size for 'd', 'u', and 'x' including padding. */
+ enum { IFMTSIZE = INT_STRLEN_BOUND(void *) };
+ char ifmtbuf[NIOVMAX][IFMTSIZE];
int niov = 0;
pid_t pid = 0;
char pidbuf[12];
@@ -143,6 +147,8 @@ _dl_debug_vdprintf (int fd, int tag_p, const char *fmt, va_list arg)
if (*fmt == '*')
{
width = va_arg (arg, int);
+ /* The maximum padding accepted is up to pointer size. */
+ assert (width < IFMTSIZE);
++fmt;
}
@@ -203,14 +209,7 @@ _dl_debug_vdprintf (int fd, int tag_p, const char *fmt, va_list arg)
#endif
}
- /* We use alloca() to allocate the buffer with the most
- pessimistic guess for the size. Using alloca() allows
- having more than one integer formatting in a call. */
- int size = 1 + 3 * sizeof (unsigned long int);
- if (width + 1 > size)
- size = width + 1;
- char *buf = (char *) alloca (size);
- char *endp = &buf[size];
+ char *endp = &ifmtbuf[niov][IFMTSIZE];
char *cp = _itoa (num, endp, *fmt == 'x' ? 16 : 10, 0);
/* Pad to the width the user specified. */
--
2.33.0
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