From ab197de19848e7241412e9f83f8a3171c3185675 Mon Sep 17 00:00:00 2001 From: Iru Cai Date: Sun, 18 Mar 2018 15:07:47 +0800 Subject: [PATCH 1/2] linux-bootstrap-5.md: fix typo, http->https --- Booting/linux-bootstrap-5.md | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/Booting/linux-bootstrap-5.md b/Booting/linux-bootstrap-5.md index 46f1e32..f10100f 100644 --- a/Booting/linux-bootstrap-5.md +++ b/Booting/linux-bootstrap-5.md @@ -187,7 +187,7 @@ At the end, we can see the call to the `extract_kernel` function: popq %rsi ``` -Again we set `rdi` to a pointer to the `boot_params` structure and preserve it on the stack. In the same time we set `rsi` to point to the area which should be usedd for kernel uncompression. The last step is preparation of the `extract_kernel` parameters and call of this function which will uncompres the kernel. The `extract_kernel` function is defined in the [arch/x86/boot/compressed/misc.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/compressed/misc.c) source code file and takes six arguments: +Again we set `rdi` to a pointer to the `boot_params` structure and preserve it on the stack. In the same time we set `rsi` to point to the area which should be used for kernel uncompression. The last step is preparation of the `extract_kernel` parameters and call of this function which will uncompres the kernel. The `extract_kernel` function is defined in the [arch/x86/boot/compressed/misc.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/compressed/misc.c) source code file and takes six arguments: * `rmode` - pointer to the [boot_params](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973//arch/x86/include/uapi/asm/bootparam.h#L114) structure which is filled by bootloader or during early kernel initialization; * `heap` - pointer to the `boot_heap` which represents start address of the early boot heap; @@ -383,10 +383,10 @@ Links -------------------------------------------------------------------------------- * [address space layout randomization](https://en.wikipedia.org/wiki/Address_space_layout_randomization) -* [initrd](http://en.wikipedia.org/wiki/Initrd) -* [long mode](http://en.wikipedia.org/wiki/Long_mode) +* [initrd](https://en.wikipedia.org/wiki/Initrd) +* [long mode](https://en.wikipedia.org/wiki/Long_mode) * [bzip2](http://www.bzip.org/) -* [RDdRand instruction](http://en.wikipedia.org/wiki/RdRand) -* [Time Stamp Counter](http://en.wikipedia.org/wiki/Time_Stamp_Counter) -* [Programmable Interval Timers](http://en.wikipedia.org/wiki/Intel_8253) +* [RdRand instruction](https://en.wikipedia.org/wiki/RdRand) +* [Time Stamp Counter](https://en.wikipedia.org/wiki/Time_Stamp_Counter) +* [Programmable Interval Timers](https://en.wikipedia.org/wiki/Intel_8253) * [Previous part](https://github.com/0xAX/linux-insides/blob/master/Booting/linux-bootstrap-4.md) From 7c0d65420c391c7419cc4e475a39c12c426c9e75 Mon Sep 17 00:00:00 2001 From: Iru Cai Date: Sun, 18 Mar 2018 15:16:34 +0800 Subject: [PATCH 2/2] linux-bootstrap-2: correct the calling convention statement The use of ax, dx, cx to pass the function arguments is not `fastcall` convention in GCC, which only uses cx and dx. This calling convention comes from the GCC -mregparm=3 option. [1] https://en.wikipedia.org/wiki/X86_calling_conventions --- Booting/linux-bootstrap-2.md | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/Booting/linux-bootstrap-2.md b/Booting/linux-bootstrap-2.md index 039ef42..ff64a20 100644 --- a/Booting/linux-bootstrap-2.md +++ b/Booting/linux-bootstrap-2.md @@ -210,7 +210,7 @@ ENDPROC(memcpy) Yeah, we just moved to C code and now assembly again :) First of all, we can see that `memcpy` and other routines which are defined here, start and end with the two macros: `GLOBAL` and `ENDPROC`. `GLOBAL` is described in [arch/x86/include/asm/linkage.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/include/asm/linkage.h) which defines the `globl` directive and its label. `ENDPROC` is described in [include/linux/linkage.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/include/linux/linkage.h) and marks the `name` symbol as a function name and ends with the size of the `name` symbol. -The implementation of `memcpy` is simple. At first, it pushes values from the `si` and `di` registers to the stack to preserve their values because they will change during the `memcpy`. `memcpy` and other functions in copy.S use `fastcall` calling conventions. So it gets its incoming parameters from the `ax`, `dx` and `cx` registers. Calling `memcpy` looks like this: +The implementation of `memcpy` is simple. At first, it pushes values from the `si` and `di` registers to the stack to preserve their values because they will change during the `memcpy`. As we can see in the `REALMODE_CFLAGS` in `arch/x86/Makefile`, the kernel build system uses the `-mregparm=3` option of GCC, so functions get the first three parameters from `ax`, `dx` and `cx` registers. Calling `memcpy` looks like this: ```c memcpy(&boot_params.hdr, &hdr, sizeof hdr); @@ -304,7 +304,7 @@ GLOBAL(memset) ENDPROC(memset) ``` -As you can read above, it uses the `fastcall` calling conventions like the `memcpy` function, which means that the function gets its parameters from the `ax`, `dx` and `cx` registers. +As you can read above, it uses the same calling conventions as the `memcpy` function, which means that the function gets its parameters from the `ax`, `dx` and `cx` registers. The implementation of `memset` is similar to that of memcpy. It saves the value of the `di` register on the stack and puts the value of`ax`, which stores the address of the `biosregs` structure, into `di` . Next is the `movzbl` instruction, which copies the value of `dl` to the lower 2 bytes of the `eax` register. The remaining 2 high bytes of `eax` will be filled with zeros.