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([2804:1b3:a7c0:17c8:f12d:93ab:bc0f:dd56]) by smtp.gmail.com with ESMTPSA id l4-20020a0568301d6400b0066c495a651dsm2008302oti.38.2022.10.31.12.01.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Oct 2022 12:01:35 -0700 (PDT) From: Adhemerval Zanella To: libc-alpha@sourceware.org, Szabolcs Nagy Subject: [PATCH] elf: Remove allocate use on _dl_debug_printf Date: Mon, 31 Oct 2022 16:01:31 -0300 Message-Id: <20221031190131.2183199-1-adhemerval.zanella@linaro.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: 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 lesser than the INT_STRLEN_BOUND(void *) (20 for LP64). This works if pointer 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 slight larger static stack, below it 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. --- 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 #include #include +#include /* 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. */ -- 2.34.1