Some compile-"Warnings" with Core v5.3.0 which I hadnt with v4.6.0

[guidol70]

On some (not all) compiles for Pico2 I do get the follwing "warnings", but the .ino does compile.
My Project doesnt use Wifi/Network - only serial and SDCard.

Do you know why this happens - and not all the time?
I read in the changelog that you did something about LWIP....,

In file included from C:\Users\guido\AppData\Local\Arduino15\packages\rp2040\hardware\rp2040\5.3.0\cores\rp2040\lwip\src\core\ipv4\dhcp.c:1:
In function 'dhcp_option_byte',
    inlined from 'dhcp_discover.isra' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1053:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
In file included from C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/arch.h:48,
                 from C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/debug.h:40,
                 from C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/opt.h:52,
                 from C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:66:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_discover.isra':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~
In function 'dhcp_option_byte',
    inlined from 'dhcp_discover.isra' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1053:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_discover.isra':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~
In function 'dhcp_option_byte',
    inlined from 'dhcp_reboot.isra' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1291:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_reboot.isra':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~
In function 'dhcp_option_byte',
    inlined from 'dhcp_reboot.isra' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1291:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_reboot.isra':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~
In function 'dhcp_option_byte',
    inlined from 'dhcp_select.isra' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:478:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_select.isra':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~
In function 'dhcp_option_byte',
    inlined from 'dhcp_select.isra' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:478:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_select.isra':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~
"C:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\tools\\pqt-gcc\\4.1.0-1aec55e/bin/arm-none-eabi-gcc" -c -Werror=return-type -Wno-psabi -DUSBD_PID=0x000f -DUSBD_VID=0x2e8a -DUSBD_MAX_POWER_MA=250 "-DUSB_MANUFACTURER=\"Raspberry Pi\"" "-DUSB_PRODUCT=\"Pico 2\"" -DLWIP_IPV6=0 -DLWIP_IPV4=1 -DLWIP_IGMP=1 -DLWIP_CHECKSUM_CTRL_PER_NETIF=1 -DFILE_COPY_CONSTRUCTOR_SELECT=FILE_COPY_CONSTRUCTOR_PUBLIC -DUSE_UTF8_LONG_NAMES=1 -DDISABLE_FS_H_WARNING=1 "-DARDUINO_VARIANT=\"rpipico2\"" -DPICO_FLASH_SIZE_BYTES=4194304 "@C:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0/lib/platform_def.txt" "@C:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0/lib/rp2350/platform_def.txt" -mcpu=cortex-m33 -mthumb -march=armv8-m.main+fp+dsp -mfloat-abi=softfp -mcmse -ffunction-sections -fdata-sections -fno-exceptions -MMD "-iprefixC:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0/" "@C:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0/lib/rp2350/platform_inc.txt" "@C:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0/lib/core_inc.txt" "-IC:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0/include" -std=gnu17 -g -pipe -DF_CPU=300000000L -DARDUINO=10819 -DARDUINO_RASPBERRY_PI_PICO_2 "-DBOARD_NAME=\"RASPBERRY_PI_PICO_2\"" -DARDUINO_ARCH_RP2040 -O3 "-IC:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0\\cores\\rp2040" "-IC:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0\\variants\\rpipico2" "C:\\Users\\guido\\AppData\\Local\\Arduino15\\packages\\rp2040\\hardware\\rp2040\\5.3.0\\cores\\rp2040\\lwip\\src\\core\\ipv4\\ip4.c" -o "C:\\Users\\guido\\AppData\\Local\\Temp\\arduino_build_617629\\core\\lwip\\src\\core\\ipv4\\ip4.c.o"
In function 'dhcp_option_byte',
    inlined from 'dhcp_renew' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1179:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_renew':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~
In function 'dhcp_option_byte',
    inlined from 'dhcp_renew' at C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1179:25:
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/core/ipv4/dhcp.c:1453:30: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1453 |   options[options_out_len++] = value;
      |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h: In function 'dhcp_renew':
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:26: note: at offset 68 into destination object 'options' of size 68
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |                          ^~~~~~~
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/src/rp2_common/pico_lwip/include/arch/cc.h:76:30: note: in definition of macro 'PACK_STRUCT_FIELD'
   76 | #define PACK_STRUCT_FIELD(x) x
      |                              ^
C:/Users/guido/AppData/Local/Arduino15/packages/rp2040/hardware/rp2040/5.3.0/pico-sdk/lib/lwip/src/include/lwip/prot/dhcp.h:90:3: note: in expansion of macro 'PACK_STRUCT_FLD_8'
   90 |   PACK_STRUCT_FLD_8(u8_t options[DHCP_OPTIONS_LEN]);
      |   ^~~~~~~~~~~~~~~~~

[earlephilhower]

That's a GCC optimizer warning issue and not real. #3154 ran into it. Seemd to only be the Cortex M3 and only O3 level. Either ignore it or send a report into the GNU mailing list or just don't use O3 for all functions, just the ones you really need it for.