[Crash-utility] zram decompress support for gcore/crash-utility

[赵乾利]

Hello list,

When i try to use gcore to parse coredump from fulldump,I got below issue that make the coredump unavailable.

1.     Zram is very common feature,in current android system supports zram swap,but gcore/crash-utility does not support,even zram swap can decoded from ram,many page fault due to this reason.
I added zram decompress feature to gcore,and i’m also considering wheather support zram in crash-utility,but for this feature,i have to add miniLZO to codebase, I'm not sure if it's acceptable,plase help give some advice.
miniLZO :miniLZO is a very lightweight subset of the LZO library,Distributed under the terms of the GNU General Public License<http://www.oberhumer.com/opensource/gpl.html> (GPL v2+).
http://www.oberhumer.com/opensource/lzo/

This change is a bit big,I attached it to the mail,if attachment is not available,you can also see these patch in github: https://github.com/zhaoqianli0202/crash-gcore/commits/upstream
Please review.


2.     For historical reasons,kernel reserved top 8/16 bytes of stacks,but after kernel-4.14, this reservation was cancelled,so gcore needs to improve compatibility.
kernel change as below:
commit 34be98f4944f99076f049a6806fc5f5207a755d3
Author: Ard Biesheuvel <ard.biesheuvel at linaro.org<mailto:ard.biesheuvel at linaro.org>>
Date:   Thu Jul 20 17:15:45 2017 +0100

    arm64: kernel: remove {THREAD,IRQ_STACK}_START_SP

    For historical reasons, we leave the top 16 bytes of our task and IRQ
    stacks unused, a practice used to ensure that the SP can always be
    masked to find the base of the current stack (historically, where
    thread_info could be found).™
====
Patch for this issue:
commit d1031df4617351a58b8edfb0121c306baaa34f9d
Author: zhaoqianli <zhaoqianli at xiaomi.com>
Date:   Mon Mar 30 12:07:02 2020 +0800

    gcore: ARM/ARM64 reserved 8/16 byte in the top of stacks before 4.14,
    but this reservation was removed after 4.14
Without this patch,gcore counld't parse full callstack in version after 4.14

diff --git a/gcore.c b/gcore.c
index f75701d..f6e1787 100644
--- a/gcore.c
+++ b/gcore.c
@@ -558,4 +558,16 @@ static void gcore_machdep_init(void)

        if (!gcore_arch_vsyscall_has_vm_alwaysdump_flag())
                gcore_machdep->vm_alwaysdump = 0x00000000;
+
+#if defined(ARM) || defined(ARM64)
+#ifdef ARM
+#define STACK_RESERVE_SIZE 8
+#else
+#define STACK_RESERVE_SIZE 16
+#endif
+       if (THIS_KERNEL_VERSION >= LINUX(4,14,0))
+               gcore_machdep->stack_reserve = 0;
+       else
+               gcore_machdep->stack_reserve = STACK_RESERVE_SIZE;
+#endif
}
diff --git a/libgcore/gcore_arm.c b/libgcore/gcore_arm.c
index 891d01e..c8aefdf 100644
--- a/libgcore/gcore_arm.c
+++ b/libgcore/gcore_arm.c
@@ -29,7 +29,7 @@ static int gpr_get(struct task_context *target,

        BZERO(regs, sizeof(*regs));

-       readmem(machdep->get_stacktop(target->task) - 8 - SIZE(pt_regs), KVADDR,
+       readmem(machdep->get_stacktop(target->task) - gcore_machdep->stack_reserve - SIZE(pt_regs), KVADDR,
                regs, SIZE(pt_regs), "genregs_get: pt_regs",
                gcore_verbose_error_handle());

diff --git a/libgcore/gcore_arm64.c b/libgcore/gcore_arm64.c
index 3257389..ed3fdc8 100644
--- a/libgcore/gcore_arm64.c
+++ b/libgcore/gcore_arm64.c
@@ -28,7 +28,7 @@ static int gpr_get(struct task_context *target,

        BZERO(regs, sizeof(*regs));

-       readmem(machdep->get_stacktop(target->task) - 16 - SIZE(pt_regs), KVADDR,
+       readmem(machdep->get_stacktop(target->task) - gcore_machdep->stack_reserve - SIZE(pt_regs), KVADDR,
                regs, sizeof(struct user_pt_regs), "gpr_get: user_pt_regs",
                gcore_verbose_error_handle());

@@ -124,7 +124,7 @@ static int compat_gpr_get(struct task_context *target,
        BZERO(&pt_regs, sizeof(pt_regs));
        BZERO(regs, sizeof(*regs));

-       readmem(machdep->get_stacktop(target->task) - 16 - SIZE(pt_regs), KVADDR,
+       readmem(machdep->get_stacktop(target->task) - gcore_machdep->stack_reserve - SIZE(pt_regs), KVADDR,
                &pt_regs, sizeof(struct pt_regs), "compat_gpr_get: pt_regs",
                gcore_verbose_error_handle());

diff --git a/libgcore/gcore_defs.h b/libgcore/gcore_defs.h
index b0f5603..f31036c 100644
--- a/libgcore/gcore_defs.h
+++ b/libgcore/gcore_defs.h
@@ -1177,6 +1177,7 @@ extern struct gcore_size_table gcore_size_table;
struct gcore_machdep_table
{
        ulong vm_alwaysdump;
+       uint8_t stack_reserve;
};
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