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ARM: 6501/1: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in mm/proc-v7.S
Directives such as .long and .word do not magically cause the assembler location counter to become aligned in gas. As a result, using these directives in code sections can result in misaligned data words when building a Thumb-2 kernel (CONFIG_THUMB2_KERNEL). This is a Bad Thing, since the ABI permits the compiler to assume that fundamental types of word size or above are word- aligned when accessing them from C. If the data is not really word-aligned, this can cause impaired performance and stray alignment faults in some circumstances. In general, the following rules should be applied when using data word declaration directives inside code sections: * .quad and .double: .align 3 * .long, .word, .single, .float: .align (or .align 2) * .short: No explicit alignment required, since Thumb-2 instructions are always 2 or 4 bytes in size. immediately after an instruction. In this specific case, we can achieve the desired alignment by forcing a 32-bit branch instruction using the W() macro, since the assembler location counter is already 32-bit aligned in this case. Reviewed-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Dave Martin <dave.martin@linaro.org> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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1 changed files with 2 additions and 2 deletions
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@ -381,7 +381,7 @@ __v7_ca9mp_proc_info:
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PMD_SECT_XN | \
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PMD_SECT_AP_WRITE | \
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PMD_SECT_AP_READ
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b __v7_ca9mp_setup
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W(b) __v7_ca9mp_setup
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.long cpu_arch_name
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.long cpu_elf_name
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.long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS
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@ -413,7 +413,7 @@ __v7_proc_info:
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PMD_SECT_XN | \
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PMD_SECT_AP_WRITE | \
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PMD_SECT_AP_READ
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b __v7_setup
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W(b) __v7_setup
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.long cpu_arch_name
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.long cpu_elf_name
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.long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS
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