linux-kernel - Re: [PATCH v5 2/6] scripts/sorttable: Have mcount rela sort use direct values

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Message-ID: <20250225104552.2acc5909@gandalf.local.home>
Date: Tue, 25 Feb 2025 10:45:52 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Arnd Bergmann" <arnd@...db.de>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-kbuild@...r.kernel.org, bpf <bpf@...r.kernel.org>,
 linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org, "Masami
 Hiramatsu" <mhiramat@...nel.org>, "Mark Rutland" <mark.rutland@....com>,
 "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>, "Andrew Morton"
 <akpm@...ux-foundation.org>, "Peter Zijlstra" <peterz@...radead.org>,
 "Linus Torvalds" <torvalds@...ux-foundation.org>, "Masahiro Yamada"
 <masahiroy@...nel.org>, "Nathan Chancellor" <nathan@...nel.org>, "Nicolas
 Schier" <nicolas@...sle.eu>, "Zheng Yejian" <zhengyejian1@...wei.com>,
 "Martin Kelly" <martin.kelly@...wdstrike.com>, "Christophe Leroy"
 <christophe.leroy@...roup.eu>, "Josh Poimboeuf" <jpoimboe@...hat.com>,
 "Heiko Carstens" <hca@...ux.ibm.com>, "Catalin Marinas"
 <catalin.marinas@....com>, "Will Deacon" <will@...nel.org>, "Vasily Gorbik"
 <gor@...ux.ibm.com>, "Alexander Gordeev" <agordeev@...ux.ibm.com>
Subject: Re: [PATCH v5 2/6] scripts/sorttable: Have mcount rela sort use
 direct values

On Tue, 25 Feb 2025 09:45:52 +0100
"Arnd Bergmann" <arnd@...db.de> wrote:

> It fixes the build issue for me. I tried booting as well, but ran
> into a BUG() when I enable ftrace. I assume this is an unrelated
> issue, but you can find the output for reference in case this is
> relevant.

Thanks, can you try this patch instead? I'll be breaking it up if this works.

This also removes the kaslr_offset() code.

-- Steve

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 27c8def2139d..fdd5ffe268de 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7004,7 +7004,6 @@ static int ftrace_process_locs(struct module *mod,
 	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
-	unsigned long kaslr;
 	unsigned long flags = 0; /* Shut up gcc */
 	unsigned long pages;
 	int ret = -ENOMEM;
@@ -7056,25 +7055,37 @@ static int ftrace_process_locs(struct module *mod,
 		ftrace_pages->next = start_pg;
 	}
 
-	/* For zeroed locations that were shifted for core kernel */
-	kaslr = !mod ? kaslr_offset() : 0;
-
 	p = start;
 	pg = start_pg;
 	while (p < end) {
 		unsigned long end_offset;
-		addr = ftrace_call_adjust(*p++);
+
+		addr = *p++;
+
 		/*
 		 * Some architecture linkers will pad between
 		 * the different mcount_loc sections of different
 		 * object files to satisfy alignments.
 		 * Skip any NULL pointers.
 		 */
-		if (!addr || addr == kaslr) {
+		if (!addr) {
+			skipped++;
+			continue;
+		}
+
+		/*
+		 * If this is core kernel, make sure the address is in core
+		 * or inittext, as weak functions get zeroed and KASLR can
+		 * move them to something other than zero. It just will not
+		 * move it to an area where kernel text is.
+		 */
+		if (!mod && !(is_kernel_text(addr) || is_kernel_inittext(addr))) {
 			skipped++;
 			continue;
 		}
 
+		addr = ftrace_call_adjust(addr);
+
 		end_offset = (pg->index+1) * sizeof(pg->records[0]);
 		if (end_offset > PAGE_SIZE << pg->order) {
 			/* We should have allocated enough */
diff --git a/scripts/sorttable.c b/scripts/sorttable.c
index 23c7e0e6c024..10aff2aeb868 100644
--- a/scripts/sorttable.c
+++ b/scripts/sorttable.c
@@ -611,13 +611,16 @@ static int add_field(uint64_t addr, uint64_t size)
 	return 0;
 }
 
+/* Used for when mcount/fentry is before the function entry */
+static int before_func;
+
 /* Only return match if the address lies inside the function size */
 static int cmp_func_addr(const void *K, const void *A)
 {
 	uint64_t key = *(const uint64_t *)K;
 	const struct func_info *a = A;
 
-	if (key < a->addr)
+	if (key + before_func < a->addr)
 		return -1;
 	return key >= a->addr + a->size;
 }
@@ -827,9 +830,14 @@ static void *sort_mcount_loc(void *arg)
 		pthread_exit(m_err);
 	}
 
-	if (sort_reloc)
+	if (sort_reloc) {
 		count = fill_relocs(vals, size, ehdr, emloc->start_mcount_loc);
-	else
+		/* gcc may use relocs to save the addresses, but clang does not. */
+		if (!count) {
+			count = fill_addrs(vals, size, start_loc);
+			sort_reloc = 0;
+		}
+	} else
 		count = fill_addrs(vals, size, start_loc);
 
 	if (count < 0) {
@@ -1248,6 +1256,8 @@ static int do_file(char const *const fname, void *addr)
 #ifdef MCOUNT_SORT_ENABLED
 		sort_reloc = true;
 		rela_type = 0x403;
+		/* arm64 uses patchable function entry placing before function */
+		before_func = 8;
 #endif
 		/* fallthrough */
 	case EM_386: