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From: Adhemerval Zanella <azanella@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] elf: Remove allocate use on _dl_debug_printf Date: Wed, 2 Nov 2022 14:31:58 +0000 (GMT) [thread overview] Message-ID: <20221102143158.1C75B3858CDB@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=40c112ed0d7d0577d2f84851c1f7b8157b3bd2f5 commit 40c112ed0d7d0577d2f84851c1f7b8157b3bd2f5 Author: Adhemerval Zanella <adhemerval.zanella@linaro.org> Date: Mon Oct 31 15:46:38 2022 -0300 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 3309 0 0 3309 ced elf/dl-printf.os * patch text data bss dec hex filename 3151 0 0 3151 c4f elf/dl-printf.os Checked on x86_64-linux-gnu. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com> Diff: --- elf/dl-printf.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/elf/dl-printf.c b/elf/dl-printf.c index 00c114002c..1b55c87cfd 100644 --- a/elf/dl-printf.c +++ b/elf/dl-printf.c @@ -27,6 +27,7 @@ #include <string.h> #include <sys/uio.h> #include <unistd.h> +#include <intprops.h> /* Bare-bones printf implementation. This function only knows about the formats and flags needed and can handle only up to 64 stripes in @@ -36,6 +37,9 @@ _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]; @@ -100,6 +104,8 @@ _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; } @@ -160,14 +166,7 @@ _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. */
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