linux-kernel - [PATCH v2 6/9] mm: Allow arch specific arch_randomize_brk() with CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP

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Message-Id: <e059e83c12b01ba7c3352162828046504e586c0c.1637828367.git.christophe.leroy@csgroup.eu>
Date:   Thu, 25 Nov 2021 09:23:28 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, alex@...ti.fr
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org
Subject: [PATCH v2 6/9] mm: Allow arch specific arch_randomize_brk() with CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT

Commit e7142bf5d231 ("arm64, mm: make randomization selected by
generic topdown mmap layout") introduced a default version of
arch_randomize_brk() provided when
CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT is selected.

powerpc could select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
but needs to provide its own arch_randomize_brk().

In order to allow that, define generic version of arch_randomize_brk()
as a __weak symbol.

Cc: Alexandre Ghiti <alex@...ti.fr>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v2: Make the generic version of it a __weak symbol instead of a messy play with CONFIG_ items.
---
 mm/util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index e58151a61255..7eb69f697b38 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -344,7 +344,7 @@ unsigned long randomize_stack_top(unsigned long stack_top)
 }
 
 #ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
-unsigned long arch_randomize_brk(struct mm_struct *mm)
+unsigned long __weak arch_randomize_brk(struct mm_struct *mm)
 {
 	/* Is the current task 32bit ? */
 	if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task())
-- 
2.33.1