From: "Arnd Bergmann" <arnd@arndb.de> To: "Yuntao Liu" <liuyuntao12@huawei.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: "Russell King" <linux@armlinux.org.uk>, "Andrew Davis" <afd@ti.com>, "Andrew Morton" <akpm@linux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, "Geert Uytterhoeven" <geert+renesas@glider.be>, "Jonathan Corbet" <corbet@lwn.net>, "Mike Rapoport" <rppt@kernel.org>, "Eric DeVolder" <eric.devolder@oracle.com>, "Rob Herring" <robh@kernel.org>, "Thomas Gleixner" <tglx@linutronix.de>, "Linus Walleij" <linus.walleij@linaro.org> Subject: Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION Date: Wed, 21 Feb 2024 16:51:26 +0100 [thread overview] Message-ID: <30b01c65-12f2-4ee0-81d5-c7a2da2c36b4@app.fastmail.com> (raw) In-Reply-To: <38c09a4b-69cc-4dc5-8a68-e5f5597613ac@huawei.com> On Tue, Feb 20, 2024, at 10:53, liuyuntao (F) wrote: > 在 2024/2/20 16:40, Arnd Bergmann 写道: >> On Tue, Feb 20, 2024, at 09:15, Yuntao Liu wrote: > # > # ARM discards the .data section because it disallows r/w data in the > # decompressor. So move our .data to .data.efistub and .bss to .bss.efistub, > # which are preserved explicitly by the decompressor linker script. > # > STUBCOPY_FLAGS-$(CONFIG_ARM) += --rename-section .data=.data.efistub \ > --rename-section .bss=.bss.efistub,load,alloc > > --- > > I think that .data.efistub represents the entire .data section, the same > applies to .bss as well, > > so i move all .data and .bss into the stub here. > Ok, I see. >> >> I guess this prevents discarding any function that has a reference >> from pv_table or ex_table, even if there are no other references, >> right? > > Indeed so, if not keep ex_table, the compilation process will result in > > an error: > > no __ex_table in file: vmlinux > > Failed to sort kernel tables Sure, and without the ex_table contents, it would not be able to recover from a failed uaccess either. > and if not keep pv_table, It can be compiled successfully, but the QEMU > boots will fail. Right. The pv_table isn't technically necessary since it can be disabled. I think it was originally introduced in order to avoid performance regressions when we introduced multiplatform kernels that can run at arbitrary physical addresses rather than having it as a build-time constant. I don't know how much difference that actually makes for performance, so turning it into a normal runtime lookup may or may not be a good compromise when building with HAVE_LD_DEAD_CODE_DATA_ELIMINATION. I have given your patch some build testing with random configurations in my build setup and it seems to work fine with gcc/binutils, but unfortunately I came across a link failure using clang/lld: ld.lld: error: ./arch/arm/kernel/vmlinux.lds:35: ( expected, but got } >>> __vectors_lma = .; OVERLAY 0xffff0000 : AT(__vectors_lma) { .vectors { KEEP(*(.vectors)) } .vectors.bhb.loop8 { KEEP(*(.vectors.bhb.loop8)) } .vectors.bhb.bpiall { KEEP(*(.vectors.bhb.bpiall)) } } __vectors_start = LOADADDR(.vectors); __vectors_end = LOADADDR(.vectors) + SIZEOF(.vectors); __vectors_bhb_loop8_start = LOADADDR(.vectors.bhb.loop8); __vectors_bhb_loop8_end = LOADADDR(.vectors.bhb.loop8) + SIZEOF(.vectors.bhb.loop8); __vectors_bhb_bpiall_start = LOADADDR(.vectors.bhb.bpiall); __vectors_bhb_bpiall_end = LOADADDR(.vectors.bhb.bpiall) + SIZEOF(.vectors.bhb.bpiall); . = __vectors_lma + SIZEOF(.vectors) + SIZEOF(.vectors.bhb.loop8) + SIZEOF(.vectors.bhb.bpiall); __stubs_lma = .; .stubs ADDR(.vectors) + 0x1000 : AT(__stubs_lma) { *(.stubs) } __stubs_start = LOADADDR(.stubs); __stubs_end = LOADADDR(.stubs) + SIZEOF(.stubs); . = __stubs_lma + SIZEOF(.stubs); PROVIDE(vector_fiq_offset = vector_fiq - ADDR(.vectors)); >>> ^ I don't immediately see what the problem is here, I hope you can address it before you send a v2. Arnd
WARNING: multiple messages have this Message-ID (diff)
From: "Arnd Bergmann" <arnd@arndb.de> To: "Yuntao Liu" <liuyuntao12@huawei.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: "Russell King" <linux@armlinux.org.uk>, "Andrew Davis" <afd@ti.com>, "Andrew Morton" <akpm@linux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, "Geert Uytterhoeven" <geert+renesas@glider.be>, "Jonathan Corbet" <corbet@lwn.net>, "Mike Rapoport" <rppt@kernel.org>, "Eric DeVolder" <eric.devolder@oracle.com>, "Rob Herring" <robh@kernel.org>, "Thomas Gleixner" <tglx@linutronix.de>, "Linus Walleij" <linus.walleij@linaro.org> Subject: Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION Date: Wed, 21 Feb 2024 16:51:26 +0100 [thread overview] Message-ID: <30b01c65-12f2-4ee0-81d5-c7a2da2c36b4@app.fastmail.com> (raw) In-Reply-To: <38c09a4b-69cc-4dc5-8a68-e5f5597613ac@huawei.com> On Tue, Feb 20, 2024, at 10:53, liuyuntao (F) wrote: > 在 2024/2/20 16:40, Arnd Bergmann 写道: >> On Tue, Feb 20, 2024, at 09:15, Yuntao Liu wrote: > # > # ARM discards the .data section because it disallows r/w data in the > # decompressor. So move our .data to .data.efistub and .bss to .bss.efistub, > # which are preserved explicitly by the decompressor linker script. > # > STUBCOPY_FLAGS-$(CONFIG_ARM) += --rename-section .data=.data.efistub \ > --rename-section .bss=.bss.efistub,load,alloc > > --- > > I think that .data.efistub represents the entire .data section, the same > applies to .bss as well, > > so i move all .data and .bss into the stub here. > Ok, I see. >> >> I guess this prevents discarding any function that has a reference >> from pv_table or ex_table, even if there are no other references, >> right? > > Indeed so, if not keep ex_table, the compilation process will result in > > an error: > > no __ex_table in file: vmlinux > > Failed to sort kernel tables Sure, and without the ex_table contents, it would not be able to recover from a failed uaccess either. > and if not keep pv_table, It can be compiled successfully, but the QEMU > boots will fail. Right. The pv_table isn't technically necessary since it can be disabled. I think it was originally introduced in order to avoid performance regressions when we introduced multiplatform kernels that can run at arbitrary physical addresses rather than having it as a build-time constant. I don't know how much difference that actually makes for performance, so turning it into a normal runtime lookup may or may not be a good compromise when building with HAVE_LD_DEAD_CODE_DATA_ELIMINATION. I have given your patch some build testing with random configurations in my build setup and it seems to work fine with gcc/binutils, but unfortunately I came across a link failure using clang/lld: ld.lld: error: ./arch/arm/kernel/vmlinux.lds:35: ( expected, but got } >>> __vectors_lma = .; OVERLAY 0xffff0000 : AT(__vectors_lma) { .vectors { KEEP(*(.vectors)) } .vectors.bhb.loop8 { KEEP(*(.vectors.bhb.loop8)) } .vectors.bhb.bpiall { KEEP(*(.vectors.bhb.bpiall)) } } __vectors_start = LOADADDR(.vectors); __vectors_end = LOADADDR(.vectors) + SIZEOF(.vectors); __vectors_bhb_loop8_start = LOADADDR(.vectors.bhb.loop8); __vectors_bhb_loop8_end = LOADADDR(.vectors.bhb.loop8) + SIZEOF(.vectors.bhb.loop8); __vectors_bhb_bpiall_start = LOADADDR(.vectors.bhb.bpiall); __vectors_bhb_bpiall_end = LOADADDR(.vectors.bhb.bpiall) + SIZEOF(.vectors.bhb.bpiall); . = __vectors_lma + SIZEOF(.vectors) + SIZEOF(.vectors.bhb.loop8) + SIZEOF(.vectors.bhb.bpiall); __stubs_lma = .; .stubs ADDR(.vectors) + 0x1000 : AT(__stubs_lma) { *(.stubs) } __stubs_start = LOADADDR(.stubs); __stubs_end = LOADADDR(.stubs) + SIZEOF(.stubs); . = __stubs_lma + SIZEOF(.stubs); PROVIDE(vector_fiq_offset = vector_fiq - ADDR(.vectors)); >>> ^ I don't immediately see what the problem is here, I hope you can address it before you send a v2. Arnd _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2024-02-21 15:52 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-02-20 8:15 [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION Yuntao Liu 2024-02-20 8:15 ` Yuntao Liu 2024-02-20 8:40 ` Arnd Bergmann 2024-02-20 8:40 ` Arnd Bergmann 2024-02-20 9:53 ` liuyuntao (F) 2024-02-20 9:53 ` liuyuntao (F) 2024-02-21 15:51 ` Arnd Bergmann [this message] 2024-02-21 15:51 ` Arnd Bergmann 2024-02-22 9:52 ` Arnd Bergmann 2024-02-22 9:52 ` Arnd Bergmann 2024-02-22 11:32 ` liuyuntao (F) 2024-02-22 11:32 ` liuyuntao (F) 2024-02-22 11:24 ` liuyuntao (F) 2024-02-22 11:24 ` liuyuntao (F) 2024-02-22 16:04 ` Arnd Bergmann 2024-02-22 16:04 ` Arnd Bergmann 2024-02-23 1:39 ` liuyuntao (F) 2024-02-23 1:39 ` liuyuntao (F) 2024-02-23 6:32 ` Arnd Bergmann 2024-02-23 6:32 ` Arnd Bergmann 2024-02-27 8:06 ` liuyuntao (F) 2024-02-27 8:06 ` liuyuntao (F) 2024-03-07 3:09 ` liuyuntao (F) 2024-03-07 3:09 ` liuyuntao (F) 2024-03-07 7:29 ` Arnd Bergmann 2024-03-07 7:29 ` Arnd Bergmann
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