| Message ID | 20200904081949.5594-4-linus.walleij@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | RFC: ARM section mapping debug prints | expand |
On Fri, 4 Sep 2020, Linus Walleij wrote: > This creates a facility to print the early 1MB section mappings > of the kernel. By selecting the symbol CONFIG_DEBUG_EARLY_MAPPINGS > we can get a printout of some of the early mappings as they > are written into the swapper_pg_dir page table during very early > boot. > > Currently I introduced hooks for printing the MMU enable 1:1 > mappings, the kernel RAM mappings and the "r2" (ATAGs or DTB) > mappings. > > The debug prints will show the physical address base and the > virtual address base map, something like this for example: > > Uncompressing Linux... done, booting the kernel. > MMU enable: 0x40300000->0x40300000 > Kernel RAM: 0x40000000->0xc0000000 > Kernel RAM: 0x40100000->0xc0100000 > Kernel RAM: 0x40200000->0xc0200000 > (...) > Kernel RAM: 0x42500000->0xc2500000 > Kernel RAM: 0x42600000->0xc2600000 > ATAG/DTB : 0x43000000->0xc3000000 > ATAG/DTB : 0x43100000->0xc3100000 > > This code does not try to be clever and shuffle registers > around like some puzzle, instead we just store out r1 thru r6 > into memory while printing and read them back afterwards. > It is debug code anyway, so optimizations are not any concern > here. > > Signed-off-by: Linus Walleij <linus.walleij@linaro.org> > --- > arch/arm/Kconfig.debug | 13 ++++- > arch/arm/kernel/head.S | 109 ++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 120 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug > index 87912e5c2256..a1620f2d0963 100644 > --- a/arch/arm/Kconfig.debug > +++ b/arch/arm/Kconfig.debug > @@ -1919,7 +1919,18 @@ config DEBUG_UNCOMPRESS > When this option is set, the selected DEBUG_LL output method > will be re-used for normal decompressor output on multiplatform > kernels. > - > + > +config DEBUG_EARLY_MAPPINGS > + bool "Enable early section mapping debugging via DEBUG_LL output" > + depends on DEBUG_LL > + help > + This option enables the kernel to print a list of all the 1 MB > + section mappings used to map physical to virtual mempory > + during the early boot. These mappings are used until the > + kernel sets up the proper page table. > + > + The selected DEBUG_LL output method will be used for these debug > + messages. > > config UNCOMPRESS_INCLUDE > string > diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S > index 8b089c4c0d17..5758a99f6f0f 100644 > --- a/arch/arm/kernel/head.S > +++ b/arch/arm/kernel/head.S > @@ -163,6 +163,109 @@ ENDPROC(stext) > .long PAGE_OFFSET > #endif > > +#ifdef CONFIG_DEBUG_EARLY_MAPPINGS > +__debug_tmp: > + .align > + .long 0, 0, 0, 0, 0, 0 /* r1 thru r6 */ You shouldn't write to the .text segment. This won't work for XIP as you'll read 0 back, or worse you'll trigger a flash memory controller operation. You should allocate your temporary buffer in the .bss section instead. Look at the printhex code for example. > +__en_mmu_debug_txt: > + .asciz "MMU enable: " > + .align > +__ram_debug_txt: > + .asciz "Kernel RAM: " > + .align > +__r2_debug_txt: > + .asciz "ATAG/DTB : " > + .align No need to align string starts. This is necessary only after the last one. > + /* > + * This macro prints one physical to virtual section map using > + * a section descriptor and a section table address > + */ > + .macro dbg_pr, secd, vindex > + /* Only the physical address in secd please */ > + bic \secd, \secd, #0x000ff000 > + bic \secd, \secd, #0x00000ff0 > + bic \secd, \secd, #0x0000000f > + /* Convert the section index to a virtual address */ > + bic \vindex, \vindex, #0xff000000 > + bic \vindex, \vindex, #0x00ff0000 > + bic \vindex, \vindex, #0x0000c000 > + lsr \vindex, \vindex, #PMD_ORDER /* Convert to index */ > + lsl \vindex, \vindex, #SECTION_SHIFT /* Convert to virtual address */ > + mov r0, #'0' > + bl printch > + mov r0, #'x' > + bl printch > + mov r0, \secd > + bl printhex8 > + mov r0, #'-' > + bl printch > + mov r0, #'>' > + bl printch > + mov r0, #'0' > + bl printch > + mov r0, #'x' > + bl printch Here I'd suggest you add the string "->0x", or even " -> 0x" for some breathing room, e.g.: __num_prefix_debug_txt: .asciz " -> 0x" Then, with the first number you use: adr r0, __num_prefix_debug_txt + 4 bl printascii and no string offset for the second number. > + mov r0, \vindex > + bl printhex8 > + mov r0, #'\n' > + bl printch > + .endm > + > + /* > + * r3 = current section descriptor, bits 31-20 is the physical address > + * r5 = section table index > + */ > + .macro dbg_pr_mmu > + adr r0, __debug_tmp > + stmia r0, {r1-r6} > + mov r6, r3 /* Save r3 to r6 (print corrupts r3) */ > + adr r0, __en_mmu_debug_txt > + bl printascii > + /* Print helper wants physical offset index */ > + lsl r5, r5, #PMD_ORDER > + dbg_pr r6, r5 > + adr r0, __debug_tmp > + ldmia r0, {r1-r6} > + .endm > + > + /* > + * r0 = section table index absolute address in physical memory > + * r3 = current section descriptor, bits 31-20 is the physical address > + */ > + .macro dbg_pr_ram > + mov r5, r0 /* Save r0 in r5 */ > + adr r0, __debug_tmp > + stmia r0, {r1-r6} > + mov r6, r3 /* Save r3 to r6 (print corrupts r3) */ A long long time ago I had a patch that shuffled registers around so that the long lived values would be kept in r4 and above so to free r0-r3 for short lived values and parameter passing to make things easier when doing this sort of thing. I don't remember if I pushed it to the patch system, and if I did probably it got outdated and I didn't refresh it. > + adr r0, __ram_debug_txt > + bl printascii > + dbg_pr r6, r5 > + adr r0, __debug_tmp > + ldmia r0, {r1-r6} > + mov r0, r5 /* Restore r0 from r5 */ > + .endm > + > + /* Debug text for "what is in r2" either ATAGs or a DTB */ > + .macro dbg_pr_r2 > + adr r0, __debug_tmp > + stmia r0, {r1-r6} > + mov r5, r3 /* Save r3 to r5 (print corrupts r3) */ > + adr r0, __r2_debug_txt > + bl printascii > + dbg_pr r6, r5 > + adr r0, __debug_tmp > + ldmia r0, {r1-r6} > + .endm > +#else > + /* Dummy stubs when not debugging */ > + .macro dbg_pr_mmu > + .endm > + .macro dbg_pr_ram > + .endm > + .macro dbg_pr_r2 > + .endm > +#endif /* CONFIG_DEBUG_EARLY_MAPPINGS */ > + > /* > * Setup the initial page tables. We only setup the barest > * amount which are required to get the kernel running, which > @@ -234,6 +337,7 @@ __create_page_tables: > mov r6, r6, lsr #SECTION_SHIFT > > 1: orr r3, r7, r5, lsl #SECTION_SHIFT @ flags + kernel base > + dbg_pr_mmu > str r3, [r4, r5, lsl #PMD_ORDER] @ identity mapping > cmp r5, r6 > addlo r5, r5, #1 @ next section > @@ -246,7 +350,8 @@ __create_page_tables: > ldr r6, =(_end - 1) > orr r3, r8, r7 > add r6, r4, r6, lsr #(SECTION_SHIFT - PMD_ORDER) > -1: str r3, [r0], #1 << PMD_ORDER > +1: dbg_pr_ram > + str r3, [r0], #1 << PMD_ORDER > add r3, r3, #1 << SECTION_SHIFT > cmp r0, r6 > bls 1b > @@ -281,8 +386,10 @@ __create_page_tables: > add r3, r3, #PAGE_OFFSET > add r3, r4, r3, lsr #(SECTION_SHIFT - PMD_ORDER) > orr r6, r7, r0 > + dbg_pr_r2 > str r6, [r3], #1 << PMD_ORDER > add r6, r6, #1 << SECTION_SHIFT > + dbg_pr_r2 > str r6, [r3] > 1: > > -- > 2.26.2 > >
On Fri, 4 Sep 2020, Nicolas Pitre wrote: > On Fri, 4 Sep 2020, Linus Walleij wrote: > > > + .macro dbg_pr_ram > > + mov r5, r0 /* Save r0 in r5 */ > > + adr r0, __debug_tmp > > + stmia r0, {r1-r6} > > + mov r6, r3 /* Save r3 to r6 (print corrupts r3) */ > > A long long time ago I had a patch that shuffled registers around so > that the long lived values would be kept in r4 and above so to free > r0-r3 for short lived values and parameter passing to make things easier > when doing this sort of thing. I don't remember if I pushed it to the > patch system, and if I did probably it got outdated and I didn't refresh > it. Found it. It is here: https://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=7234/2 Nicolas
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index 87912e5c2256..a1620f2d0963 100644 --- a/arch/arm/Kconfig.debug +++ b/arch/arm/Kconfig.debug @@ -1919,7 +1919,18 @@ config DEBUG_UNCOMPRESS When this option is set, the selected DEBUG_LL output method will be re-used for normal decompressor output on multiplatform kernels. - + +config DEBUG_EARLY_MAPPINGS + bool "Enable early section mapping debugging via DEBUG_LL output" + depends on DEBUG_LL + help + This option enables the kernel to print a list of all the 1 MB + section mappings used to map physical to virtual mempory + during the early boot. These mappings are used until the + kernel sets up the proper page table. + + The selected DEBUG_LL output method will be used for these debug + messages. config UNCOMPRESS_INCLUDE string diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S index 8b089c4c0d17..5758a99f6f0f 100644 --- a/arch/arm/kernel/head.S +++ b/arch/arm/kernel/head.S @@ -163,6 +163,109 @@ ENDPROC(stext) .long PAGE_OFFSET #endif +#ifdef CONFIG_DEBUG_EARLY_MAPPINGS +__debug_tmp: + .align + .long 0, 0, 0, 0, 0, 0 /* r1 thru r6 */ +__en_mmu_debug_txt: + .asciz "MMU enable: " + .align +__ram_debug_txt: + .asciz "Kernel RAM: " + .align +__r2_debug_txt: + .asciz "ATAG/DTB : " + .align + /* + * This macro prints one physical to virtual section map using + * a section descriptor and a section table address + */ + .macro dbg_pr, secd, vindex + /* Only the physical address in secd please */ + bic \secd, \secd, #0x000ff000 + bic \secd, \secd, #0x00000ff0 + bic \secd, \secd, #0x0000000f + /* Convert the section index to a virtual address */ + bic \vindex, \vindex, #0xff000000 + bic \vindex, \vindex, #0x00ff0000 + bic \vindex, \vindex, #0x0000c000 + lsr \vindex, \vindex, #PMD_ORDER /* Convert to index */ + lsl \vindex, \vindex, #SECTION_SHIFT /* Convert to virtual address */ + mov r0, #'0' + bl printch + mov r0, #'x' + bl printch + mov r0, \secd + bl printhex8 + mov r0, #'-' + bl printch + mov r0, #'>' + bl printch + mov r0, #'0' + bl printch + mov r0, #'x' + bl printch + mov r0, \vindex + bl printhex8 + mov r0, #'\n' + bl printch + .endm + + /* + * r3 = current section descriptor, bits 31-20 is the physical address + * r5 = section table index + */ + .macro dbg_pr_mmu + adr r0, __debug_tmp + stmia r0, {r1-r6} + mov r6, r3 /* Save r3 to r6 (print corrupts r3) */ + adr r0, __en_mmu_debug_txt + bl printascii + /* Print helper wants physical offset index */ + lsl r5, r5, #PMD_ORDER + dbg_pr r6, r5 + adr r0, __debug_tmp + ldmia r0, {r1-r6} + .endm + + /* + * r0 = section table index absolute address in physical memory + * r3 = current section descriptor, bits 31-20 is the physical address + */ + .macro dbg_pr_ram + mov r5, r0 /* Save r0 in r5 */ + adr r0, __debug_tmp + stmia r0, {r1-r6} + mov r6, r3 /* Save r3 to r6 (print corrupts r3) */ + adr r0, __ram_debug_txt + bl printascii + dbg_pr r6, r5 + adr r0, __debug_tmp + ldmia r0, {r1-r6} + mov r0, r5 /* Restore r0 from r5 */ + .endm + + /* Debug text for "what is in r2" either ATAGs or a DTB */ + .macro dbg_pr_r2 + adr r0, __debug_tmp + stmia r0, {r1-r6} + mov r5, r3 /* Save r3 to r5 (print corrupts r3) */ + adr r0, __r2_debug_txt + bl printascii + dbg_pr r6, r5 + adr r0, __debug_tmp + ldmia r0, {r1-r6} + .endm +#else + /* Dummy stubs when not debugging */ + .macro dbg_pr_mmu + .endm + .macro dbg_pr_ram + .endm + .macro dbg_pr_r2 + .endm +#endif /* CONFIG_DEBUG_EARLY_MAPPINGS */ + /* * Setup the initial page tables. We only setup the barest * amount which are required to get the kernel running, which @@ -234,6 +337,7 @@ __create_page_tables: mov r6, r6, lsr #SECTION_SHIFT 1: orr r3, r7, r5, lsl #SECTION_SHIFT @ flags + kernel base + dbg_pr_mmu str r3, [r4, r5, lsl #PMD_ORDER] @ identity mapping cmp r5, r6 addlo r5, r5, #1 @ next section @@ -246,7 +350,8 @@ __create_page_tables: ldr r6, =(_end - 1) orr r3, r8, r7 add r6, r4, r6, lsr #(SECTION_SHIFT - PMD_ORDER) -1: str r3, [r0], #1 << PMD_ORDER +1: dbg_pr_ram + str r3, [r0], #1 << PMD_ORDER add r3, r3, #1 << SECTION_SHIFT cmp r0, r6 bls 1b @@ -281,8 +386,10 @@ __create_page_tables: add r3, r3, #PAGE_OFFSET add r3, r4, r3, lsr #(SECTION_SHIFT - PMD_ORDER) orr r6, r7, r0 + dbg_pr_r2 str r6, [r3], #1 << PMD_ORDER add r6, r6, #1 << SECTION_SHIFT + dbg_pr_r2 str r6, [r3] 1:
This creates a facility to print the early 1MB section mappings of the kernel. By selecting the symbol CONFIG_DEBUG_EARLY_MAPPINGS we can get a printout of some of the early mappings as they are written into the swapper_pg_dir page table during very early boot. Currently I introduced hooks for printing the MMU enable 1:1 mappings, the kernel RAM mappings and the "r2" (ATAGs or DTB) mappings. The debug prints will show the physical address base and the virtual address base map, something like this for example: Uncompressing Linux... done, booting the kernel. MMU enable: 0x40300000->0x40300000 Kernel RAM: 0x40000000->0xc0000000 Kernel RAM: 0x40100000->0xc0100000 Kernel RAM: 0x40200000->0xc0200000 (...) Kernel RAM: 0x42500000->0xc2500000 Kernel RAM: 0x42600000->0xc2600000 ATAG/DTB : 0x43000000->0xc3000000 ATAG/DTB : 0x43100000->0xc3100000 This code does not try to be clever and shuffle registers around like some puzzle, instead we just store out r1 thru r6 into memory while printing and read them back afterwards. It is debug code anyway, so optimizations are not any concern here. Signed-off-by: Linus Walleij <linus.walleij@linaro.org> --- arch/arm/Kconfig.debug | 13 ++++- arch/arm/kernel/head.S | 109 ++++++++++++++++++++++++++++++++++++++++- 2 files changed, 120 insertions(+), 2 deletions(-)